If an oldish computer check the air vents for dust and fluff.If any inside will probably need cleaning as well.
Have you tried Tapping F8 as the Computer starts just to see if it will start in safe mode that way. Check in device Manager to see if it finds any faults and event viewer to see if any problems on there.
Maybe do a chkdsk to see if that is ok.
And have you ran your security programs,Malwarebytes is good at finding problems.