Try cleaning out your cookies, cache, temporary system files, prefetch, bad registries & temporary internet files with CCleaner or Anvi System Cloud Booster. Maybe that will help. If it doesn't, have you changed the number of processors in msconfig? If you changed from 1 to e.g. 8, then your computer will slow down & instead it will use 256MB of RAM instead of what you have in your computer. One more thing, try scanning for viruses with Windows Defender, or Anvi Smart Defender. I hope this helps you.
- MrXtreme