First, uninstall any unneeded programs that you have installed. If you happen to have more than one antivirus installed, remove all but one. Once that's done, then run "Disk Cleanup" to remove all the junk files on the computer. Once that's done, run "chkdsk" using the instructions below.
Try running Chkdsk in "repair" mode to find any damaged files and correct them. Start by opening a command prompt as an admin. RIGHT click on the Start button, choose "Command Prompt (Admin). (Or type "Command" in the search line, then RIGHT click on the "Command Prompt" listing at the top, choose "Run as admin".) Once there, type chkdsk /f /r /x, leaving the appropriate spaces between the letters as shown, then press the Enter key. You should see a note that it can't be run till a restart is done, type "Y" for yes, then press the Enter key again. Close the command prompt and restart the computer. Chkdsk will run upon restart and will take quite a while to finish.. Don't panic when the progress bar stays at 10% for a long time. It's fairly normal and the Chkdsk process may take a couple of hours.
When it's finished, it will boot to your normal startup/lock screen and you can login normally and then see if things are working correctly again.
After after running chkdsk, then defrag the computer.
Hope this helps.
I reinstalled win 8 for a week but now use it feel very slow, start the machine it takes more than 2 minutes to operate the new stable. Shutting down the machine takes more than a minute to complete. I checked the machine without virus and software running underground. Please help me, I thank.
Machine Configuration: Asus
CPU: intel core i5 5200U
GPU: Nvidia Geforce 930M
OS: Windows 8.1 64 bit