The symptoms you are having suggests an overheating problem, probably caused by dust in and around the CPU fan. Here's how to do it without disassembling your whole laptop.
Tools needed:
* Magnetized tiny phillips screwdriver.
* Very small TORX or small flat blade screwdriver.
* Heatsink paste (optional but recommended).
Instructions:
1. Turn off your system.
2. Turn it over and find the small square cover on the bottom that covers the CPU. When the laptop is upright this would be in the in the upper left corner of the computer.
3. Remove the four screws and remove the cover. You should see a small aluminum square, this is the heatsink and the clogged cooling fins.
You will need a little tiny TORX driver or a very small straight screwdriver to get these four screws of the cover out. Be careful where you put these screws as they are very small and easily lost.
4. You should see four screws across the top and bottom of the heatsink. Remove ONLY the four "outside" screws, do not remove the two screws in the middle of each edge. The heatsink will now lift off of the processor. Use a magnetized screwdriver and DO NOT DROP those little screws into the computer or you will have to remove the entire cover.
5. Notice how much gunk is on the fan end of the fins. Blow softly through the OTHER end of the fins and blow the crud out of there.
6. Put a small amount of heatsink paste on the CPU surface before replacing the heatsink.
7. Replace the screws holding down the heatsink and replace the CPU cover. You are done and should notice large volumes of only warm air from the vent now.
This should return your monitor back to normal operation.