... get an all blue screen full of text that includes a message
Driver_irql_no_less_or_equal

Further down it has a string of numbers that start
Stop:0x000000D1

Is all this supposed to help me fix it?

So far as I can recall the only new software or hardware, is an upgrade to Norting Internet Security (from NIS 2003) and installation of the software for an Olympus digital camera that we gave our boy for Christmas.

I don't defrag often, but the computer is seeming slow and I thought this would speed it up.

The hard disc is 35% free on a 40gb total, but it is about 5 years old and the PC is used a lot, so could it be this slowing things down if it's on the way out?