Virus-ridden computer: PLEASE HELP!

[alyssaw]

Hi there!
Recently my Dell Studio 1555 laptop with Windows Vista Home Edition has been going crazy. In normal mode (with all the startup programs enabled) it runs very slowly, freezes constantly and then brings up blue screens that are "dumping physical memory", no programs will work due to how slow it runs and due to reboots. When I turn on the computer I get pop-ups about start-up programs that are unable to work, "windows user defender" being unable to work, and something called "symantec" being unable to work. It works when I disable all of the start-up programs, however. I'm currently in Safe Mode with Networking to write this, but I can't figure out what to do to fix my laptop so that it's back to running like new. I feel like I've tried everything:
1) I attempted to first run several virus scans using both AVG and SUPERantispyware Free Edition; neither found any threats.
2) Then I tried to run a Startup Repair with my burned Vista Repair Disk, but it doesn't have a Repair option when I F8 it at startup, just a "debugging mode" and a few other safe modes.
3) I tried to run a System Restore. When I try to run it, it says that there are no restore points. I tried to manually make one, but my "System Protection" tab is missing in my System Properties and I can't figure out how to get it back.

I am in need to my computer ASAP due to needing to finish my online classes. So, thanks for anyone who can help at all!