|You mentioned 3 things...one of them is the problem.|
1. you changed CMOS - what does that mean? You changed the battery? Or you entered the settings menu & changed things around? Improper CMOS settings can screw up a system.
2. you changed the RAM - are you 100% sure it's compatible? Is there more than one RAM stick installed? Did you try the new one by itself? Did you try it in different slots? Does the system work with just the old RAM installed?
3. heatsink is hot - it's supposed to get hot....that's it's job! The heat from the processor "sinks" into the metal base them flows to the fins & gets blow away by the fan. If it's TOO hot, then there's a problem. Is it dirty or dust clogged? is the fan working properly? Did you knock it loose when you were messing with the RAM?