I am currently runnig P4 HT 3.0GHZ on a Machspeed 865PEDAP motherboard.
The MB has 2 memory slots, DIMM1 and DIMM2. I bought pair of dual channel kit brand new retail 2x512 (Kingston Value Ram). When I plug them both in, computer doesn't boot. But when I plug in DIMM1 only, it works. When I plug in DIMM2 only, it doesn't work. My gut feeling tells me that my DIMM2 slot is messed up but it could be a simple mistake.

I've tried to run dual channel with other matching sticks of memory prior to the dual channel kit i just bought, and it had the same outcome. Can someone help? Thankyou

Yes , faults in the slots is a huge possibility . You should get that checked .

Also there could be problem with one of the RAMs .

Check each ram module separately in each ram slot, see if pc boots.
eg. Test each module in ram slot 1 first. If only one module fails to boot that module is defective. If all modules succed to boot in slot 1 then all modules are ok. Now check the other three slots using just one module in one slot at a time. This should determin which, if any, slot is down. If all slots are ok and all ram modules are ok then you have either a compatability/timing problem or possibly a voltage/PSU problem.
Hope this helps. All the best Craig

PS better to use just two slots for dual channel performance.

memory sticks are not the problem they work fine when put in 1 at at time

i want to try to flash the bios with update but i don't have a floppy drive. anyone have a clue?

Some motherboards support USB devices on boot - consult your motherboard documentation and if it does, you can simply boot using a USB stick loaded with the appropriate flash utility.

Alternatively, you can create Boot CD's, though this is a slightly more time consuming process - same end result, though.