Have the same laptop bought about the same year. I upgraded to 2gig of ram but hadn't seated the RAM properly in one of the slots, and the laptop didn't boot properly, it beeped at me once then sat there.
It is kind of fiddley putting the RAM in so I would look to see if you have seated them correctly. I thought I had, I even had got them to go flat and click into the retainer but they had not interfaced with their connectors correctly.