Hi,
Is the computer slow when booting up or is it slow on everything?
- If the computer is slow in everything I would suggest reinstalling Windows 7 first.
- If the same problem will persist after reinstalling Windows 7 that could only mean that it's a hardware problem.
- Do consider replacing the HDD as well that might be the cause of the problem.
- Try cleaning the inside as well and remove all the dust off the fans and apply new thermal paste on the CPU and GPU.
- And lastly, if the laptop needs a repair if all these will not work.