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This is a common issue that many users face while upgrading their Mac to a new operating system. The solution is quite straightforward and easy to tackle. To fix this issue, you have to delete the existing macOS Sierra installer and re-download it. To do so, open Launchpad and you should see the.

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Firefox's add-on update check may be blocked by the security software as well. The Mozilla Firefox web browser is not the only program that is affected by issues though. Spotify's Web Player may not be able to connect to Spotify for example with Avast 2015 running on the system.

Like any computer, a Mac is prone to serious problems over the course of its life. A wide variety of things can go horribly, horribly wrong. From a complete failure to start to that terrifying kernel panic screen, here's how to troubleshoot (and hopefully fix) what's plaguing your Mac.

For the most part, the problems you run into on a Mac are pretty universal across all versions of OS X, but we'll stick to the most modern operating systems here: Lion and Mountain Lion (most of these tips should also work with Snow Leopard though). If you're still covered by Apple's warranty or AppleCare, the easiest solution is to walk into the Apple Store and have them fix everything for free. If you don't want to waste time or you're not covered anymore, you can do a lot of the troubleshooting yourself.

The Problem: Blue or Grey Screen on Startup

When you turn on your computer and get a grey or blue screen (or it gets stuck at the Apple logo) that never loads OS X, it's a pretty good cause for concern. This can happen for a number of reasons, so it's one of the most frustrating things that can happen to a Mac, and troubleshooting it is no easy task. So, let's break it down into a few steps you can take to figure out what's going on.

Step One: Disconnect All Peripherals

One of the main causes of a grey or blue screen on startup is incompatible hardware connected to the machine. This might be a printer, an external hard drive, or even a USB hub. So, disconnect everything except the mouse and keyboard, and restart your computer.

If your Mac starts this way, then it's an issue with one of those peripherals. You have to trial-and-error your way through to figure out which one, so connect them back into your computer one by one, and restart. If one of them causes your computer to hang on the grey screen again, you've found your issue.

If you figure out the problematic peripheral, it's time to do a little research. Head to the manufacturer's web site and see if others are reporting the same problem. You might be able to fix it with a software update or a firmware update to the device.

If no devices are causing problems, and your Mac still won't boot, then it's time to dig a little deeper.

Step Two: Perform a Safe Boot

Safe boot makes your Mac boot up with the minimum amount of drivers needed to make it work, and it checks your hard disk in the process (it might take a bit longer to boot up). Do do this, start up your computer while holding down the Shift key until the Apple logo passes. If your Mac starts up with the safe boot, go ahead and restart the computer again and see if it boots up normally (as odd as it sounds this fixes the problem a surprising amount of the time). If not, it's time to give the hard drive a closer look.

Step Three: Run Disk Utility

If you still can't boot up OS X normally, it's time to run Disk Utility and check out your hard drive:

Boot up your computer while holding down Command+R (if you're running Snow Leopard or earlier, find your OS installation disc, put it in the drive, and reboot your computer holding down C). This will boot you into a diagnostic mode.
Select the Disk Utility Option.
Select your hard drive, and click 'Verify.' Wait for Disk Utility to finish running.
If problems pop up, click 'Repair Disk.'
If nothing pops up, click 'Repair Permissions' and wait for Disk Utility to scan your hard drive again.
If Disk Utility finds and repairs some problems, go ahead and reboot.

In a lot of cases, running Disk Utility will catch problems with startup issues. Sometimes a single file with the wrong permissions can cause the whole system to collapse, or if something's not in the right place it won't boot. If this doesn't work, you have a lot more problems to look into.

Further Resources

If the above solutions don't work, it's time to dig a lot deeper into your system. Your problem could range from a bad hard drive to a faulty logic board. Here are a few more steps that should help you single out the problem:

The Problem: Persistent Beach Ball

Ah yes, the spinning beach ball that refuses to go away. Sometimes it's a small, application-specific problem that's easy to solve, but other times it's part of a much bigger mess. If your Mac is tossing up the spinning beach ball consistently, it's time to figure out the exact cause.

Step One: Check Activity Monitor

Your Mac will usually get a spinning beach ball when it's somehow overloaded. More often than not, this just lasts a few seconds and goes away, in which case you can ignore it. If it doesn't, the best way to figure out what's going on is to launch Activity Monitor and pinpoint which program is causing the problem.

If you need to, force quit any programs that are potentially causing the beach ball (Command+Option+Esc).
Launch Activity Monitor (Applications > Utilities).
Now go about your daily usage. If the beach ball comes up, switch over to Activity Monitor and see which app is taking up the biggest CPU load (oftentimes this will spike at 100%).

If it's a powerful piece of software like Photoshop that's causing problems, then it's a good chance you need more RAM in your computer. RAM can help with multi-tasking issues, and if the beach ball comes up when you're running a few programs at once additional RAM will help (this is very easy to install yourself). If not, and it's something lightweight like a file syncing service like Dropbox or an instant messenger client like Adium, then it's probably a problem with the software itself. Try quitting the app and seeing if the problem persists. If the beach ball doesn't return, then you have your problem. Check the developer's web site to see if they've issued an update, run Software Update (Apple Logo > Software Update), or get in touch with the developer if no update is available.

Another possible problem is that your hard disk is getting close to full.

Step Two: Reclaim Hard Drive Space

When your hard disk is full it can cause spinning beach ball problems. For a lot of us, this just means cleaning up two folders: your trash and your downloads folder:

Right-click the trash can icon and select 'Empty Trash.' If you have a lot of stuff in there or you haven't done this recently you might get enough space to save your file.
Now head to your downloads folder (Users > Your Name > Downloads). Go through and delete any files you no longer need.

In a lot of cases, doing the above two steps can free up enough space to continue working. That said, you might still need to free up even more space. To make this process easy, we likeDisk Inventory X. With Disk Inventory X, you can look at your hard drive and find the biggest space hogs quickly so you can delete them and m

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