When booting the computer turns itself off a few times before giving a message saying the sysytem failed booting at checkpoint [EMem]. If i persist in turning it on and off it will boot up Windows but it can just turn off at any time. I've checked that there is nothing loose from the hardware to the motherboard, anybody got any clues?

It sounds like defective memory. You should run memtest from the boot prompt of a Knoppix CD or swap in some known good memory. If you still have the problem after verifying the memory, post back.

hi buggz thank for the reply to the post but it wont let the system run atall as soon i switch it on it doesnt let me go into the boot up log it just switches the system off, i think it mite be the heat sink but im not sure.

any other suggestions.

Have you run through the steps in the My PC Won't Start sticky at the top of the forum? I do't think the heat sink would prevent the PC from booting unless it has already caused the processor to overheat and damaged it. Try stripping the system down to the essentials (Motherboard, processor, 1 stick of memory, display card, and power supply and then see if it will post. This will help eliminate other things like bad drives or other add-in cards. Also disconnect any external devices except the monitor and keyboard/mouse. Let me know how that works out.

You probably have failed caps on the mobo per info on Dell forum: http://forums.us.dell.com/supportforums/board/message?board.id=oplex_bios&message.id=8930