I just assembled a D620 from spare parts. The LCD, MB, CPU, DIMMS and heatsink are new. The rest of the components are from other system repairs.

On power up, the system LEDs light up as normal then after about 5 seconds, it shuts down. We never get to the Dell splash screen. My first guess would be the processor but this is new and Im temporarily holding off on that. My first practical guess may be the fan or modem as Latitudes tend not to even post if there is a problem with one of these 2 parts (these parts are suspect as they have been sitting around for a while and I cant remember whether they were working when I got them or not).

Any other suggestions on what to swap out first?

I do realize, though, that even though the MB and CPU are new, they could still be dead. I'm playing the numbers right now on that in all probability they are not the problem. I will test the CPU Monday at work on another machine.

Well, its fixed. I went back and opened it up, looked everything over to make sure everything was connected properly. When I booted, it fired right up. I got the OS installed, no problem. After a while, when I was rebooting, it did the same thing again. I opened it and all I did was open and retighten the processor screw and she fired right up with no problems since.

yeah she was probably overheating if the heatsink wasnt properley contacting the CPU