Dell XPS M1210 won't boot after processor upgrade

Hi folks!
I've got a Dell XPS M120 with the Intel T2300E processor (1.6 GHz). Because it got slower over the years I decided to upgrade a few things. I upgraded the RAM which now consists of two 2GB units. Next I bought an SSD. Finally I wanted more processing power so I boughte the Intel T400 (2.16 GHz) which should be compatible.
I dismounted the whole laptop and installed the new processor, making sure I added enough thermal paste. I reassembled it and after turning it on, the following happened:

I pressed the power button. The lights go on for about 2 seconds, and then it shuts off again. The display remained off and the CPU-fan doesn't even start spinning.

I thought that it could be that the BIOS needet to be updated so I re-installed the old processor. Sadly, the same thing happened.

Dear forum, please advise me what to do. I'm desparate. What could it be? Did I break the whole thing? Isn't there enough power (my battery's busted so I keep it plugged in to the wall)? Is the motherboard damaged? Or maybe the socket?
I love this laptop so much and I would love to see run with an SSD, more RAM and more processing power.

Thank you very much in advance!
Rafael

 

If you put the old chip in and got the same then either you left something disconnected, reconnected something leaving a loose connection or killed it. reseat everything else and if you still get the same take a close up of the processor socket and link it here.

 

Thank you for your answer!
I disassembled it again but it still won't boot up...
Here's a close-up of the socket:


( http://abload.de/image.php?img=sockett7req.jpg)

 

I would reseat the ram, it often gets bumped and won't boot because it's slightly out of alignment. Also you can try clearing CMOS by removing the CMOS battery and pressing the power button for a few seconds.