to determine if its adapter issue try to replace your 60w to 85w and try to turn on w/o the battery, if still same problem try to insert your battery and plugin the adapter 60w or 85w (don't turn on) it must have charging indicator and light indicator in the battery is blinking. if is charging, both 60w and 85w are good. try booting w/o the ram check if the power light indicator goes blinking. pls let me know the result.
did you check the RAM first? Update: if your imac having display problem after minor troubleshooting assessment i think your problem is in the logic board, the gpu chip. i recommended let the tech guy to do a re-balling the gpu/bga chip not just reheating using heat gun, or if you want to do a test you can use a heat gun to your gpu, just heat 10sec to the gpu chip and try to test, if you have the display probably it was bga problem