From your description, you are unable to remove the CPU and heatsink
from the motherboard.
There should be three slots on one side of the heatsink retaining
clip. They interact with three plastic notches on the CPU mount. This
device presses the heatsink against the CPU.
To remove the heatsink and CPU:
1. Follow all safety procedures to prevent electric shock and
electrostatic discharge.
2. Using a small flat-head screwdriver, depress the heatsink retaining
clip until the three slots disengage from the CPU mount. You will
probably have to help the slots disengage. Warning: be careful not to
hit the motherboard or the capacitors with your hands or the
screwdriver.
3. Once you have the heatsink retaining clip removed you can remove
the heatsink. If it is stuck and you are unable to remove it, remove
it with the CPU. The CPU is in a ZIF socket, so just lift the lever
and pick up the assembly.
Take great care to not bend the CPU pins.
Check your motherboard's documentation to verify the layout before you
start
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