start up problem

So my brother had a desktop he messed up and went to get a lap top.He gave me his desktop cause he knows nothing about a computer other then how to get virus's and look up lord knows what on them to get the virus's. The computer starts up fine but starts the windows load and goes completely black. I have tried booting in safe mode and it shows all the numbers and freezes. The desktop is older ..its a HP Pavilion a6042n Desktop I know some about computers but I am no pro to be honest. I was thinking of taking the drive out and just replacing it then reloading his vista or a copy of xp on there. Can the drive be Dbaned and then be used or is it once a drive seems messed up theres no use to it? I have like 6 computers around the house and basically use my lap top for my medical work for work...the desktops are basically used for when the girl comes over to play games on but thought that a6042n would stiill be worth saving....advice?