As your PC gets used more and more it collects programs, junk, malware, errors, extra files and so on.
This takes it´s toll and often the best (only true way) to make it as good as new is the reinstall windows.
This is can be destructive so it’s best to have your files have to be backed-up or they could be destroyed. We can help or do this all for you. It doesn’t have to be destructive and the only thing required in this case is that you have sufficient hard drive space. The minimum amount free hard drive space is: ~10GB (Windows XP); ~20GB (Windows Vista); ~15GB Windows 7).