Backup will not complete in order to restore windows, please help

I have a Dell Inspiron N5010 with Windows 7 Home Premium 64bit. First off, I have been trying to install updates on my computer and they keep failing. Since my computer has been acting sluggish. I have tried installing them one at a time and the windows repair tool and neither has worked. The next step is to restore windows correct? In order to restore windows I need to backup my files on the computer on a DVD-R or an external hard drive. I have tried running the back up on a Sandisk Verbatim 4gig flash drive and it is not working. It doesn't display any error messages or anything, it just says "back up did not complete successfully". I am not a guru by any means, just in college and trying to get my computer back up to speed before the next semester. Pleas help, anything regarding getting my computer running right again would be beneficial. Thanks!

ok i updated my system info and ran the scan now in the command prompt and this is what it showed:

"Windows Resource Protection found corrupt files and successfully repaired them. Details are included in the CBS.log windir\Logs\CBS\.log. For example C:\Windows\Logs\CBS\CBS\.log.

The system file repair changes will take effect after the next reboot.

C:\Windows\system32>"

I'd suggest running the sfc /scannow at least once more to make sure there aren't any other damaged or corrupt system files (you should get a prompt at the end of the scan that Windows Resource Protection Found No Integrity Violations.)

i tried to install the updates again and they failed...

i ran scannow again and it showed that it found no integrity violations and i dont think i installed the service pack how do i do that?

no it was one of the 5 that are failing to download. i am trying to download it now by just trying it by itself