Rundll32.exe is a legit Windows program. The trouble is that viruses like to masquerade as the program and cause all sorts of operating problems: everything from causing errors on start-up and close-down to overheating the system. I am not suggesting that this is the problem in your case but I would suggest the following -
Put the system into Safe Mode on start-up (F8) and run Malwarebytes or any Anti-Malware that you have on your computer.
Also read this click here - there is a "FREE scan for errors" located at the top of page - use this at you own discretion.