External HDD Problem

Hi

I recently purchased a Seagate 160GB Hard Drive (not sata) with a Gemini External HDD Enclosure. Drive installed fine, i formatted it and began to use it. Then i removed the hard drive. But the next time i tried to switch on the computer, the MoBo wouldn’t perform POST (no beep). I turned it off, connected the external drive, and voila! it started. So basically my computer does not start up without the external hard drive. I have:
(a) Seagate 80GB (not SATA) on Primary Master
(b) DVD -RW on Secondary Slave
(c) Gigabyte GA-K8N51GMF-9 mobo
Can anyone please suggest how to fix the problem? Thanx in advance..

Kedia