|Have you, or is it possible someone else who had access to this computer...|
- dropped it, or dropped anything on it, or otherwise exposed it to a physical jolt ?
- spilled liquid on it, or sprayed it with liquid, or exposed it to liquid such as rain ?
Since it last worked properly all the time, has there been a power failure event that happened while the AC adapter was plugged in ?
Those things are the most frequent reasons something inside the laptop has been damaged.
You need to supply as much detail as you can come up with regarding what you symptoms are.
What are you seeing ?
Is Windows loading to the desktop screen ?
Try pressing F8 repeatedly while booting and loading
Safe mode. or Enable VGAc mode, or Last known good..
Try removing the battery and running it with only the AC adapter connected.