Doby

This is very hard to answer because it could be either, could you post a link to the new psu? If its a very low quality just plugging in the video card could draw it down enough to make the computer do that.

I suggest you try another video card if you have one or can barrow one from a friend or the same with the psu.

It should be one of the two because it was a very good sign that you got beeps with the video card removed but to pinpoint witch it is without swapping parts would only be a guess