|First thing to do is to change the setting in Vista to automatically restart. See the link below to learn how.|
Then you can post the error code/s here for help with them.
In the meantime you can do several things.
Open the case and see if there is lots of built up dirt/dust. If so, get a can of compressed air or use a compressor to blow out everything. Blow out the power supply from both ends.
You may want to move the tower to a better location. This will be messy. Be sure the computer is unplugged. DO NOT use a vacuum cleaner. Static discharge can kill the computer.
Once inside, examine the motherboard for bad capacitors. :You are looking for bulging tops or leaking capacitors. See the link below for photos.
Next, you can run a memory test on the RAM. Download memtest86+ from the link below. Use the ISO.zip file for installation on a USB flash drive if the computer can boot from a USB device. You will need to reset the boot order to boot to it.
You can also run a hard drive fitness test.
Run scannow SFC. See the link below to learn how.