Couple of things to try before you format and rebuild.
You dont say what version of windows you use.
If still using 98

apart from having your head examined you could hit start/run and type "SFC"
This runs a utility that restores any system files that have been corrupted. You will need a 98 disc with service pack two on it to restore the files.
If on XP or vista both have restore and are worth a try at restoring to an earlier date.
Also you mentioned a faulty gfx card. If you installed a new one are you sure you uninstalled all drivers and utilities for the old one. For example with a radeon card there can be 4 different programs to uninstall before you can install the new one.
The graphics properties of a pc are called upon to do absolutely everything on a pc as anything you do affects the screen. This means a pc can crash at any time doing anything if the wrong drivers are installed and it can look like a programme fault when in fact it was the graphics drivers. Also make sure you have the latest drivers.
Sisoft sandra do a nice programme to test performance of individual components and you can get a demo version for nowt.
If you are really brave and computer literate try searching for "EBCD torrent" in google. Its a host of very usefull test items but a lot of them run in dos before windows boots so you do need to know what you are doing. Its a very powerfull disc which for example can find and change any password on your computer to what the operator wants

It may also be listed as "hirams boot disc" USE WITH CARE YOU CAN DO SERIOUS HARM IF YOU DONT KNOW WHAT YOUR DOING.
Finally if its a specific programme that crashes thing and gives an error message try googling the error code ..it often throws up answers.
PM me if you need further help.
Cheers
Dave