Windows 7: Problematic Backup, Causing Boot Errors and Blue Screens

I have been using (I know, don't laugh) a Dell Inspiron 1525 for several years, and it has been running perfectly and without issue. In July of this year, I upgraded to Windows 7, backed up the original Vista OS to a 2TB external hard drive, and deleted it from the hard drive with no trouble. The computer continued to run flawlessly...except that at some point, it as accidentally set to save scheduled backups to the D Drive, which was quickly maxed out by the backups.

Last month or so, I changed the backups to save to my external hard drive, which is permanently attached to the computer. Since then, five or six times I have left my computer on standby and returned to find a black error screen that informed me that my computer cannot find a drive to boot from. Upon restarting the computer, it booted and ran normally.

About a week ago, my computer froze, and had to be hard shut down and restarted (something that has never in my memory happened to this computer). Upon reboot, it again worked fine.

This evening, the computer froze similarly, and then went to a dreaded blue screen...the screen identified a "kernel" error, and advised me to check any newly-installed software or other harmful devices on the computer. I allowed it to catalog the error and restart, and it functioned normally for about thirty minutes, at which point it promptly went to the black error screen (skipped the freeze) and then to the same blue screen.



I'm letting it run its memory test and repair right now. I have always kept this computer in immaculate condition and until today it has run as well as the day I brought it home. It is possible that the sudden errors are unrelated to the backup issue, but it is the only error I've had and the only notable change that has been made to the computer.

I apologize for the lack of specifics as far as the error messages go...I wasn't expecting things to go awry so suddenly and wasn't prepared to write everything down. Does this issue sound familiar to anyone? What can I do to fix this poor computer? I'm completely stumped.