Computer shutting down and flashing?

I have a emachines W3400. I just installed a new Sata hdd and a IDE lighton disc drive. It was working fine for a while then while I was doing something it made a loud pop and shu off and the power on led just blinks untill I unplug the tower and plug it back in. Then it does it durning startup. I unplugged the hdd and it continued. I unplugged the new disc drive too and it seems to be working fine now. Any ideas on the culprit?