Computer wont boot

Hello,
I am having a problem getting my computer to boot. the first thing that started to happen was if i left it on overnight it would lock up and i would have to manually shut it down. after a few of these lock ups it stopped booting up. I have been able to get to the bios screen maby 6 times out of 100 powering it on and off. the only way that it has gone past the bios screen seems to be when i have my recovery disk in. the first time this happened i just let the disk load the windows properties and then cancelled the recovery the computer worked fine for a few hours. the next day back to the same thing no bios screen just a black screen. i have been trying for two weeks to get it to boot have seen the bios screen a couple of times but it would just lock up there. then yesterday i put the recovery disk in and it got me through so i zapped the hard drive and went through with the recovery. everything was working fine lastnight. this morning i try to turn it on again and it locks up on the bios screen and the next time nothing. all of my fans are running but nothing. when i do get it to run it runs great but the start up is the problem. i hope someone can help me here.