e1505/6400 locks up

My inspiron e1505 locks up randomly and sometimes won't turn back on..  It seems to do it more often when it is moving around like when I just lift it up to put it on my lap or put it on my desktop.  When it doesn't turn back on, it will turn on the power light, and spin up my hard drive but after about 3 seconds will just shut off.  No post, no lock codes, nothing.   I am a dell technician but I just need some extra brain power because I have used the Dell Solution Network to it's max. 

I know it's not my ram.  I have reseated them plenty of times as well as switched with known good ones and it still does the same thing.  It could possibly be the ram slots though, I don't know.  I have reseated my video card as well.  Pretty much the only thing I haven't reseated is the processor (next on my list).

I try to run 32 bit diags, but it freezes in random spots just like it does within windows and it has never given me any error codes.  I also ran the crash analysis tool but it didn't find anyting that could help.  I am okay with replacing a part but I need to find out what part I need replaced since I don't have a valid warrantee anymore. I am thinking it is either my motherboard or my video card. (More motherboard becuase when it won't turn back on I pull out the battery and drain the flea power it seems to start up just fine.)

Any suggestions?

Also if it is the video card, what can I upgrade to?  I use my lappy for graphic editing and design and could use the extra power.

Thanks in advance!