hello friends,

this is guru,i have a problem with my harddisk.it is not detecting.
actually before i have removed my harddisk & again i joined it as it was.
when i switch on my computer, fan automatically stops within a sec.the motherboard light remains on but neither the bios occurs on the screen nor fan runs.

even though i tried it as slave by connecting with other pc,but then also the other pc does not boot

If "neither the bios occurs on the screen nor fan runs" your hard drive is not an issue at this point.
More likely an issue with your power supply.
Do you hear any "Beeps"?
Is this a new problem? Did this computer work ok previously?
I would remove all devices save the RAM, CPU, Graphics card. Check all connections, power etc. If the CPU fan is not working don't leave the power on.
What is the make & model of the motherboard?