Dell Inspiron 4000 Laptop Shuts down during boot

Hello group, This is my first post here. I have a Dell Inspiron 4000 that the motherboard was damaged. I bought a used board on ebay for it (It was actually a 4100 motherboard as I wanted to get a little more speed) anyway, When I put it together with the new MB, It will start to boot, but shuts off after 10 seconds or so, just long enough to get to the first set-up screen. My first thought was that the Heatsink might not be properly seated on the uP, but when I took it back apart I checked it carefully and it is screwed down about as tight as it can be, and doesn't appear to have any side higher then the other. The original MB was a Dell 002UH with a PIII Mobile 850 uP, the new board is a Dell AP515 with a Celeron 1.2Ghz.
Does anyone have any ideas what to check?
Thanks in advance for any help you can give.

 

Bump

 

Update, I was cruising Ebay again and noticed a slight difference on the heatsinks between the 4000 and the 4100, it looks like there is a "lip" around the top piece of the heatsink on the 4100, so now I am back to thinking that I may be having a thermal issue. I will update again when the new heatsink is installed.

 

Two things to check,have a look in bios usually del or f2 some time also refered to as setup and see if your motherboard has any health monitoring to check CPU temp,after 10mins of idling in the bios see if the heatsink is getting warm to the touch if so theres a good chance you have good contact with the cpu

If your bios has fail safe\best performance options try them both,remove any uneeded add in cards modems\sound cards ect also any extra cdroms and the floppy drive,you need only the harddrive your installing windows on and the cdrom,if you still have no luck only use one stick of memory in slot 0,still no luck try some different memory if you have any,you may

Welcome to the forum

 

Ahhhh! laptop sorry kinda limits your options as to what can be removed,you may be able to remove the modem or wireless adapter,if you have two sticks of memory try each seperately

 

Thanks Rikky,
But I can barely see what is on the first page of the BIOS before it shuts itself down.
I do have two sticks of RAM, They both worked fine in the old 4000 MB but the new 4100 MB says one of them is unsupported. (Two different brands). I will have to wait till Monday to try a couple of other sticks I have at work.
I also bought a 4100 heatsink on ebay, I have a hunch that is what my problem is.