Replaced Thermal Paste Now Not Booting

At this point you'll need to back track your actions to see what you failed to plug in or install correctly. Did you use an ESD mat and use proper ESD protection? In the winter months the air is very dry and static is a very big problem (ESD).

"Sal Torre, since you are getting the right POST beep code, I would try this next :""try this:""Certain changes in BIOS settings (such as chipset timing or latency, memory timing or latency, processor clock frequency, etc.) can cause a system to no longer boot.

If you are able to enter the BIOS Setup by pressing F2, reset the BIOS to factory defaults by pressing F9. Save and exit the BIOS Setup.

If you cannot enter the BIOS Setup, clear the CMOS:

Turn off all peripheral devices connected to the computer.

Disconnect the computer’s power cord from the AC power source (wall outlet or power adapter).

Remove the computer cover.

Locate the battery on the board.

With a medium flat-bladed screwdriver, gently pry the battery free from its connector. Note the orientation of the “+” and “-” on the battery.

Wait one hour then replace the battery.

Replace the computer cover.

Plug the computer and all devices back in.

You may also need to perform a BIOS Recovery after clearing the CMOS."" from here with more info about your motherboard."

"If you changed the thermal paste then in most case scenarios you had to remove the heat sink correct?

when putting the Heatsink back on did you screw it in evenly criss cross pattern or if its a clipped kind. is it tilted?

That would cause the CPU to lean in the socket.

CHECK YOUR ARM TO THE CPU SOCKET TO SEE IF IT'S LIFTED UP. THAT WOULD CAUSE THE CPU THE NOT BE ENGAGED IN THE SOCKET"