Something wrong with my computer

Im having problems with my PC for weeks ago. Since the problem starts im getting like lag or low frame rating (20FPS even playing low requirements games like LoL or Borderlands) but Windows Task Manager say that all resource’s use are low, CPU 9-10%, memory 20-25%, GPU like 10-15%. I looked for a virus, I formated Windows (thrice), I checked that I have actualized drivers, I removed GPU and installed it again, tried to play offline in case the internet its the problem, but everything remains and I dont even know what to try cause I dont know if is GPU problem, hardware, software, memory or what, so any suggest or help is appreciated.

Technical information:

  • Intel Core i7-6700k
  • 16GB RAM DDR4
  • Nvidia Geforce GTX 1080 8GB
  • Windows 10 Pro

If you need more info just ask.