Please Please Help

I have a bit of a wierd one here. Please dont get bored with this im desperate for help.
My pc takes a few times to switch on before it posts the bios, then manages to load desktop succesfully. Everything runs fine and can play games all day. My sig was:

XP2400 @ 2332mhz - 14 x 166
Asus A7N8X motherboard
2 x 256mb sticks Nanyo pc2700 @ cas2 2-2-5 (running sync)
Hercules 9700 Pro @ 351 / 662
Soundblaster Live
Modem
2 small hard drives both 5400rpm and ata100
samsung cd writer
samsung dvd drive
Thermaltake hardcano fan controller
slk800 heatsink with delta screamer 80mm
3 x normal 80mm fans in case sucking out
2 x 120mm enermax fans blowing in
Power supply cwt 460watt

Now today i have swapped my pc2700 memory for 2 sticks of 256mb pc3200 kingmax. Now with same settings as above, i get various things happening when i switch it on.
Looping re-boots, biosrom checksum errors, just wont boot at all.
If i take out one stick of memory it boots fine, and ive tried both doing this, so isnt faulty memory. Just need to know why is it doing this after just changing my memory to a better quality type.
I think its because of low quality PSU and its just got a bit much for it, with all the overclocking and everything.
What do you guys think, need a 550w Enermax.
I really really hope someone can help, im at my wits end. I bloody knew i shouldnt have upgraded.

Many thanks in advance.

bump

Did you try resetting the bios? What are the 12v, 5v, and 3.3v at when your computer is only running with 1 stick of memory?

When it boots succesfully with 1 stick , the voltage lines seem ok, 5v=4.89, 12v=12.5, and 3.3v=3.31
I also reset cmos for 30 secs. Then reset everything to defaults and boots up fine. Its Just when i put all my overclocks back to what they were when i had my pc2700 in.

Thanks for reply, any more suggestions anybody.

4.89 seems like it may be a bit low, that's under idle I'm assuming? Have you measured it under load, or just while in the bios or idling in Windows? Are you sure the new memory you got will run at cas 2 (I know it's pc3200, but I've had sdram that would go up to 150 mhz but wouldn't do cas2 at 120)?