Computer won't power up with additional hard drive attached.?

My pc originally ran with 3 hard drives, a DVD drive, and a radeon 9800 pro video card. The video card I thought was going to bad so I decided to try to replace it with a Radeon 1650 pro. While booting with the new vid card attached, I noticed my 500gig didn't have a power cord hooked up so I hooked it up while... show more My pc originally ran with 3 hard drives, a DVD drive, and a radeon 9800 pro video card. The video card I thought was going to bad so I decided to try to replace it with a Radeon 1650 pro. While booting with the new vid card attached, I noticed my 500gig didn't have a power cord hooked up so I hooked it up while it was booting, making my pc then shut down. Now the computer won't power up with all 3 HD's attached, even with old video card. Only way it will power up is with the 2 160 gig HD's, the DVD, and vid card attached, OR just 500 gig HD by itself with nothing else powered/hooked up. Did I cause a short? Power supply failing?
Update: I have a 400w power supply. I just purchased a 500w and the pc does the same thing, boots up only with the 500 gig disconnected. Keep in mind it used to boot before I possibly shorted my 500gig HD.
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