I'm not too new to computers, I've built PC's for years. But this is something I've not encountered, and I cannot source the problem. I'm thinking either the new PSU is faulty or the motherboard is bad. (or it's as simple as a bios setting)

I just recently bought a new tower and radiator to upgrade from some junk tower and a thermaltake radiator that came with a kit. just about everything else is the same, I just moved from one tower to the other. Now, when I went to power it up I got nothing. realizing I had added a few more fans because of the tower switch it was probably just a little too much for my 550w PSU. so I upgraded that to a silverstone 850w. Yay works!...but...

This is the weirdest symptom I've seen. once I shut it down, I have to unplug it for a few MINUTES and plug it back in for it to turn on. otherwise I get a flash of juice once, than nothing...

is it a bad batch of the PSU?

It is near time to replace the hardware, but I was hoping to wait until fall.

tower I'm using:
LIAN LI Lancool PC-K62 Black 0.8 mm SECC, Plastic + Mesh ATX Mid Tower Computer Case

and the PSU
SILVERSTONE ST85F-P 850W ATX 12V v2.3 / EPS 12V 80 PLUS SILVER Certified Modular Active PFC Power Supply

here is my out of date hardware:
ASUS P5KPL-AM/PS LGA 775 Intel G31 Micro ATX Intel Motherboard
Intel Pentium E5200 Wolfdale 2.5GHz LGA 775 65W Dual-Core Desktop Processor BX80571E5200 (with a weak overclock to 3.0 never breaking 45c)
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-4GBPQ

the video card is even older, but I know that's not the problem.

ALSO this is water cooled if that makes any difference on what I could have toasted or over stressed. It's a bigwater 735 kit with a video waterblock and a new 2x140mm radiator.

I am grateful for any tips/suggestions/ideas...anything. I'm at a loss as to what this is as it works...it's just odd. I'd be happy to provide any details I could be missing to my setup, just let me know.

anyone? I dont want to rma the power supply if thats not it...? thanksIssues like this are usually the board or power supply as you guessed.
Try a BIOS update if you can, often an updated BIOS can fix these issues.
If that doesn't help, you're back to square one, but really the best thing to do is try to borrow another PSU to test with, or try your PSU on another system.
What was your old PSU, out of interest?As Calum said, it is likely a PSU issue, however it could also be a problem with the CMOS not storing your setting correctly, perhaps due to a dead battery. It is common (particularly with overclocked systems) for a computer to refuse to BOOT if there are problems with BIOS settings. By unpugging the power for a few minutes the CMOS will lose the stored information and revert to default BIOS settings at the next boot. If you are overclocking, try leaving everything at default in the BIOS. If this fixes things, it is likely a dud CMOS battery. Quote

By unpugging the power for a few minutes the CMOS will lose the stored information and revert to default BIOS settings at the next boot