the mobo have a 4pin connecctor? if it does did you connect the cable to it?
put the ram back in , try resetting the cmos there are 2 ways to do this
1) the jumper , theres a jumper near the battery while the pc is off put it to pins 2-3 for about 10 seconds then put back to pins 1-2 and power up
2) disconnect the cable from the psu (the cable thats between the wall socket to the psu) and get the battery out for 30 minutes then put it back & connect the cable & power up (put the battery back exactly as it was before you got it out,do not put it on the other side) , if #1 didnt work then go for #2 , anyway if youll get it to work and youll see a message like "cmos checksum error" then get into bios and load optimized/performance/setup defaults. save & exit
if the mobo dont have a 4pin connector or it does and the cable was alredy connected to it and resetting the cmos didnt help, then its gotta be the psu or mobo , get a digital multimeter and measure the psu voltages with it and report back with the voltages, see these guides
check for bad capacitors,see examples
if youll find any they can be easily replaced at any electronic repair shop it wouldnt cost much