|I just checked Crucial & your system does accept up to 2GB RAM, 1GB per slot. But since you have a Celeron, you should be running the RAM at 133MHz (266MHz DDR).|
CL (aka CAS) is the latency. The lower the number, the faster the RAM. CAS2 is fastest for DDR1 memory, CAS 3 is the slowest. Most people get either CAS 2.5 or CAS 3 because CAS 2 is *usually* much more expensive.
Make sure you didn't knock something loose when you were playing around in the case. It sounds like you unplugged a couple of fans or at least knocked the plugs loose & they're not being detected.