Infected computer, not sure what it is

There is something going on behind the scenes on my desktop computer. Here is the system info needed:

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows XP Professional, Service Pack 3, 32 bit
Processor: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz, x86 Family 6 Model 30 Stepping 5
Processor Count: 4
RAM: 3063 Mb
Graphics Card: NVIDIA GeForce 9500 GT, 1024 Mb
Hard Drives: C: Total - 475378 MB, Free - 20187 MB;
Motherboard: MSI, P55-GD55 (MS-7589)
Antivirus: None

The computer will turn itself off and doesn't allow me to connect to the internet. It likes to turn off in Safe mode and has also turned off during a virus scan. I have tried various things to fix the problem. I downloaded some portable scanners to a usb to try and scan the machine, but none of them will run. Combofix freezes every time. Others that are .exe files, like Norton Power Eraser, will not even open. They do not appear in the folder with the same icon. I removed my virus scan software in one attempt to fix the internet connection issue. Figured it was pretty useless anyway since it had not been able to update in over 6 months.

I will stop messing with it now and await instructions.

Thanks!