When you install use the key from the computer case.

After installation see if you find c:\windows\system32\chkdsk.exe If it’s missing copy it from c:\windows\system32\dllcache to c:\windows\system32

Download a fresh copy of ComboFix and scan. Also scan with WinPFind and save the log. Then post those two logs plus a fresh HJT log.

Keep the computer off line as much as possible except to download the tools, post the logs, or get Windows updates.