Unusal harddisk problem

i have three hard drives one 80 GB pata, one 500GB pata and one 250 GB sata..
last night all of a sudden my pc stopped working.. The machine was not at all responding. I removed all the HDD and connected them one by one. But the problem persisted. When i remove the HDD the machine starts and shows no HDD attached as usual..but when HDD are connected even one at a time the machine does,nt even start!!!!!!
Dunno what the problem is ...if any one could suggest a solution i would really be grateful..thank you!!

My rig is as follows-
AMD athlonx2 4200+
Mcp61 board Zebronics
8800gt gfx 512mb
cm500 watt psu
2gb ddr2 ram

I think your PSU failed

Try changing PSU or borrow a PSU from your friend to check

Try using the same HDD using some other SATA/IDE cables. And report here.

Dunno what the problem was my psu is allright.
and the HDD started working again dunno how..thanks both of you
couldnt reply coz i was away for some time.