If you are trying to backup your WordPress site and for some reason it's not working, there are a few things that could easily be going wrong.
You might have too many large files, you might not have enough disk space or your webhost might be low on memory.
It's very to figure out which of these problems is stopping you from backing up your site.
First of all, look at your WordPress site and find out if you're using more than one Backup plugin.
This is a very common problem where you use two or more Backup plugins at once.
Don't do that.
Just choose one WordPress backup plugin to do what you need because otherwise what happens is Backup plugin number 1 backs up your 100 MB site into a new 100 MB file, backup plugin number 2 backs up your whole WordPress site including that original backup, now you have a 200 MB file.
Then backup plugin number 1 backs up your site again and backs up this 200 MB file and now you have a 400 MB site and you can see the size of your website is doubling and doubling and then eventually, it's too big to even back up.
Only use one Backup plugin.
If at all possible, store your large video files outside of your WordPress folder or even offsite such as on Amazon S3.
A very easy thing to check is to see if you have enough disk space which means if you have enough room on your website to actually store the backup.
Your website should take up less than half of the allotted space, which means if your website is 500 MB of space available, then your actual website should be under 250 Megs.
If you have a 300 MB website and you're trying to back it up in a 500 MB account, it's not going to work because you would need 600 MB total because you need room for the actual website and the same amount of room for the backup in order to store both at one time.
Make sure and log into your control panel and usually in the left-hand side they will show you how much disk space is available and how much disk space you're actually taking up.
Also make sure and contact your webhost and ask how much memory you have and if your Backup plugin errors out or stops with a message about being low on memory, it means that it does not have the speed it requires to make the backup.
In many cases contacting your web host will fix the problem.
They can change one setting and allow WordPress and your Backup plugin to use more memory and now your backups will run successfully.