I upgraded my CPU the other day. When I turn the PC on, it froze on start-up with LEDs 3 and 4 on, indicating a memory failure. I took out one of the DIMMs (both were 4 GB), and the PC started up successfully. I ordered a new DIMM, but when I tried to install it the same error occurred. It turns out that all the DIMMs work in slot 2 but none in slot 1.

During a Google search I found someone with a similar problem (although not with a Dell) who was advised to do a CMOS reset. Is this worth a try? I'm reluctant to do anything that risks causing further problems unless it has a good chance of success.

The manual states the maximum RAM as being 2×4 GB, but I've seen people say they've successfully used 8 GB modules. Is this a case of those modules working but not having been tested by Dell at the time the manual was written?