I have been having an issue with my self built system, not sure if it is hard drive, virus or software conflict.

1- A month ago I started experiencing slow start up and afterwards there would be system hangs and the HDD light would be on for a while before system response.
2- Last week started having black screen on start up then I would get the Windows start up screen for a split second then login screen comes up.
3- From Saturday I would have problems loading web pages. The page would load fully but there would be no functionality i.e cant click on links, videos wont play(have to reload the page for it to work), clicking on Google prediction links the browser hangs or crashes.
4- Today I have been getting Windows Explorer crashes when I open recycle bin.
5- Biggest problem though is programs are not showing in Programs list in the Control panel but all programs start up normally but.
6- Of late games have been also stuttering. Battlefield 4 mantle also stopped working now using DirectX and GTA 4 not loading textures.

Any help will be appreciated