Hi - I think it would be worth running this tool (System File Checker) to see if it finds / corrects anything...just follow the on screen instructions for Windows7...
https://support.microsoft.com/en-us/kb/929833
Another check worth making is open a new User Account (Control Panel-User Accounts) copy a few files into the new account and see if behaviour is normal there.
You said you had tried all the suggestions in earlier posts - did that include a system restore? (as suggested by John John) - Thanks...R
P.S. The post from GTS came in as I posted - the second account test would back up his theory, which incidentally, reminds me I have seen something similar on a laptop with a failing motherboard.