Dozer
Depending on how this thing is behaving, you may can start you computer in "safe" mode, and copy any needed files to a thumb drive. Then erase the whole machine down to empty. Reinstall the operating system and one by one reinstall the programs you need back on the machine.
After you get the machine totally erased you will need an OS. If you have to go and buy an OS then you may be better off just trashing the machine and starting over with an upgraded computer. What I did because I do my consulting work on my personal laptop was just to buy another laptop and make sure each one is totally backed up. I have long periods of time when I do not need a machine but when it is end of project time and the client is due the report then I have to be operational. Also I can take the old laptop hunting and not worry about destroying it with dust or bacon grease or bullet holes.
