These symptoms are typical of a laptop with a heat and/or power issue. Get a can of compressed air and use it to remove the dust that builds up in the fan intake and exhaust ports. Spray the air directly into both ports. Make sure your system is not powered up when you do this.
Also, make sure your battery is fully charged or the AC adapter is connected.
If these suggestions fail to help, you can always remove the hard drive from the laptop and connect to another system (with the proper adapter/enclosure) to wipe the drive. Last, there is the hammer method (pretty effective, but rather draconian).