Try this 1.
1) If you have placed the CPU FAN without removing the old thermal compound
and applying a new one on the processor then remove the old thermal
compound from the processor and make sure that your CPU FAN is also clean
without any thermal compound.
Now freshly apply some thermal compound in the middle of processor and
fix the CPU FAN properly.
2) Regarding the display issue, remove the RAM from the slot, clean it and place
it back properly or try another slot.
3) If the problem still exist then if you are having two RAMs then remove it,
place only one RAM and check if you are able to start your laptop without any
issue. If the problem still exists then try the above procedure with the other RAM.
Check your RAM also. Even bad RAM will result such problems.