There are several steps to take
1. Boot into the safe mode and run anti-virus and anti-malware
2. If you have recently installed a program remove it and see if the problems gone
3. If you are using XP or newer operating system use a restore point before the problem started
4. Boot to your Operating System disk and run system repair.
5. If nothing has worked to this point it is now time to format and reinstall your Operating System. You should have received a restore disk with your computer. Install it - boot to your optical drive and follow the instructions--no need to pay someone to do it for you.
If you have questions try back to us and we will try to answer them. Ralph