I tried to hook it up to a monitor and pressed all the dn+ f1-f12 keys
Do you mean Fn key as suggested, third button to the left of the space bar.
and nothing happened and when I run it with no ram I hear no beeps
This may be a MB or CPU issue then, if it was the onboard video chip with the issue you should have got error beeps with no Ram inserted, just to confirm when the laptop was functioning correctly did you get a POST beep? In case there is no onboard speaker on the MB.
After cleaning the fan before reassembly did you check that the fan was working correctly if at all, if the fan is not connected or not functioning the MB if it has a thermal sensor will shut the system down to prevent damage to the CPU and other components.