PC will not turn on....plugged into power supply

Please start by working through this HP support article for your power issue. Having said that, the most likely culprit in such cases is the power supply itself. Even if some lights are lit, it could be bad. You can have it tested easily by a local computer tech, who can load test it to be sure it has indeed failed, and usually provide you with a replacement for about $30.00. If you want to investigate testing it yourself, see the links to do so accessible from this general startup troubleshooter.

I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
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blinks when? right after you turn it on?
any way try removing the bios bettery for a copple of hrs and incase, remove the video card(if u have a build-in u dnt have 2 :)), and the memory(ram)...and wait a bit, then try again.....

Actually, the blinking is a troubleshooting code. HP and Compaq computers bling and sometimes beep a different sequence of codes. If you find the troubleshooting codes for that certain pc on HPs website then it will tell you exactly what is wrong and what you need to replace.