I recent invested in a new PSU to give me more juice for overclocking. The PSU in question is the Thermaltake ToughPower TX 875W (The second, improved edition.)
My other components are:
6GB Mushkin DDR3 RAM
I removed my old PSU and installed the new TT one, double and triple checked the cables were correctly placed
24 pin Mobo
8 pin CPU power
both 6pin PCI-e.
HDD, DVD Rom additional case fans.
When I turned the PC on, all fans would begin spinning, GPU fan powers up. All fans powered from Mobo headers power up too. I get the POST beep and then the computer continues in that state for 10-15secs then I get another beep as if the PC has restarted.
I checked the cables again with no luck. reinstalled my old PSU and no luck either.
Sounds like you popped something pulling out the old PSU, likely got an ESD in a bad place. I suggest you go thru the standard troubleshooting drill, pull everything off the board except the cpu and power it up, should get a pattern of beeps complaining theres no ram. put in one stick at a time doing a boot up in between...rinse repeat, just step through all the bits till you find one that wont let it boot to next level