Turn everything off, let it sit a while. While it's sitting, unplug/replug everything. Unplug unnecessary stuff in there too, in case a lower load on the power supply will help. Consider swapping in a new drive cable.
If it doesn't work the next time, put it in an IDE to USB adaptor (You do have one of those right? They're like $20) and see if another computer will recognize it and spin it up over the USB connection.
If it still doesn't work, you have 2 options. Send it to a drive recovery place and for $1000 they'll recover your data by pulling the drive apart in a clean room and putting the platters in another hard drive case. Or try the freezer trick. Wrap the hard drive in a plastic bag, with an ide cable and power cord splitter attached but the end of the cables sticking out of the bag. Squeeze all the air out of the bag, and do something to seal the end of the bag around the cables (rubber bands, silicone glue, whatever). Put the drive in the freezer and let sit for a few hours. Pull out of the freezer, but leave inside the bag to help prevent condensation from forming as the drive warms up. That's why you squeezed all the air out before sealing the bag btw. Attach to the computer while still cold, and power it up and see if it works.
I've heard of this working for long enough to copy the entire drive contents, and I've heard of guys who had to refreeze the drive a dozen times because it only worked for a few minutes each time before it warmed up too much to work. In any case...
THE FREEZER TRICK IS A LAST RESORT IF YOU HAVE NOTHING TO LOSE
