You need a good diagnostic program and a system monitor. The monitor to check the system for heat. Try "speedfan" for system heat monitor.
SpeedFan - CNET Download.com. You can tell us the results and we can help you solve the problem. The symptoms sounds like heat. You can blow out the dust from the system with a can of compressed air. Most laptops suffer from heat problems A system should be cleaned every 6 mos from dust accumulation
-
Tell us the make and model of your system and we can find information on how to open and blow out the dust.
-
falcon