Strange Problem

[Snatchers]

Okay so i have this wierd problem with a new build.

SO when i turn on the machine the fans etc spin up to speed and then it turns off and backon again ( apparently this is normal for some setups) and does the same but doesnt boot or post. If i leave it like this for a few minutes then turn it off and on it will boot.
Ive tried testing all the ram individually, no ram ( get the beeps) no gfx card (get the beeps). All the components seem fine.
Ive ran memtest for 18 hours just to check it wasnt the memory.
Once its on the system will run fine until its turned off for more than few minutes then i have to go through the same process.
Does anyone have any idea whats causing this?

System:

core 2duo e6700 at standard speeds
4Gb Patriot PC-2 8500 Extreme Performance
Asus p5q
Hiper Power 580w
Saphire 4870
creative x-fi

[mac124]

Asus mobos tend to do the turn off, turn on when booting when overclocked. This in mind i'd suggest you reset the cmos?

You may need to manually put in the memory settings afterwards to get it running at the proper speed / timings seeing as you have "Extreme Performance" memory.

[alexnifty]

Sometimes after I have changed clockspeeds it will do the on/off/on thing but it shouldn't be doing it every time.

Mac's idea about the memory timings is a good one, also check that they are getting the right voltage. Performance RAM usually needs something like 2.2v so check your RAM specs and set the timings and voltages manually. Auto will just undervolt.

[Snatchers]

Should have mentioned that i had tried inputting the proper ram speeds and voltages. Tried 2.1v , 2.2v and 2.3v all at the 1066mhz. If i do this it runs fine as normal but when i turn off it wont boot after that and i have to reset the CMOS. So for the moment im having to just run it at auto settings.
Thanks for the input so far though folks.

[ianf]

I just has the same problem this morning with an asus board (everything turns on briefly, then off, then back on again but doesn't post - however I didn't try leaving it on for a few mins and rebooting).

I had 4 x 2gb Corsair memory. I got the beeps after removing them all. It then booted with just 2 sticks in.

Asus P5Q-E
Q9550
4 x 2GB Corsair
Asus HD3650 GPU
OCZ StealthXStream 600W PSU

Update: I've narrowed it down to one seemingly faulty memory stick. Are you sure your memory is not at fault?