Please help me with my problem

Hi everyone, i've got a problem and i need your expertise. I'll try to make this as short as possible. My cousin's computer broke, win 95 wouldnt boot. she gave it to me to fix it, so i formated it and installed 98, 98 installed fine, but at the last step when it's building a driver info thing it freezes. Since it does this when i put the hard drive in my other comp, i deducted that the problem must be the HDD. so, i went out and got a 2gb HD from one of those comp shows, and try to put that in the old system. when i put it in the old system, it wont even start up... really weird since i dont see how having a HD just plugged in could hinder a whole system, anyway, it boots up fine with the origonal HD. so i put the new HD into my other comp, if i change the boot order so it boots of :a or it wont boot with the new HD in. when i boot of the HD i get this win 98 thing and then the C: prompt, i cant acess anything in it, cant format either. when i type a:\ the A: drive light comes on but it says invalid or bad disk. also i'm wondering if the A drive could be faulty....dont know what to do..... sorry this post is so long. i would very much appriciate any help that you could give me. thank you. also does anyone know a good link to a prog that makes basic boot disks that just format the HDD? the one i'm using isnt all that great. thanks again.