so i just bought a new hard drive because my old one wouldnt turn on or anything and i needed a new one anyway. so im trying to install it and it wont turn on either. power is going to all the fans and lights but not to the hard drive. help!

Standard troubleshooting tips:

1. Remove all devices except those necessary for boot (HD, video, etc.)
2. Change power connectors to HD, preferably a connector you know works.
3. Check the voltage levels on the Molex connector.
4. Check that you're not overtaxing your power supply.
5. Try HD in a different system, if possible.
6. Use an external drive case, if available.
7. Verify BIOS settings.

Granted, these aren't all necessarily going to do anything, but they are things to consider when troubleshooting: keep your options open and don't limit yourself. Sometimes the problem is weirder than you'd expect.