Welcome to LQ!
You say no 'beeps' or other visual activity so try entering the BIOS and see if anything has been changed. If you can enter BIOS then the basic system is still functional. If not then you have issues that could be power or even system board problems.
Power system off, remove power & battery then open memory access to re-seat the memory. Please use caution when removing memory and re-inserting each. When you replaced fan, what was the condition of the heat pipe for the processor?
If you can enter BIOS then you could try a LIveCD/DVD
and pressing F12 for a boot menu or enter BIOS to select the boot drive.
are good to have on hand whenever you need to test a piece of equipment. Both LiveCD have good diagnostic sets to help you.