Issue with replacing Studio 1737 motherboard, system hangs/locks up

Hi all,

I'm having a frustrating problem with my Dell Studio 1737.

The RAM clips on my motherboard have been broken for a while, and one of the RAM modules keeps popping out of place, effectively reducing my RAM by half.

A new motherboard was delivered yesterday, and I replaced it, I thought successfully.  Once I restarted the system last night with the new motherboard, everything worked fine.  I shut down the system last night.

This morning, when I booted up, the system made it to the Windows login screen, but the keyboard was inputting VERY slowly.  Like one key would enter about every 7-10 seconds or so.  Finally, I was able to log in to Windows, but immediately upon logging in, the mouse wouldn't move, and I couldn't use any keyboard shortcuts.  

I tried rebooting, and no effect.  I shut the system down and made sure all the connections were in place securely.  I even took out the heat sink and made sure the processor was seated properly.  

I rebooted again, and it worked perfectly, no lag, no freezing.  So at lunch, I shut down the system, and just now I booted up again, but it's having the same problem, freezing, lagging, no input, etc.

Does this sound like something that's fixable?  It seems that whenever I reboot the second time, the system freezes, but when I remove the processor and reseat it, and do the same with the RAM, it gives me one successful boot.

Should I update my BIOS or something or should I just replace with the old motherboard.  I thought switching the motherboard was fine, and did it succesfully on my old Studio 1747.