Have you had any malware of any type that you have gotten and rid yourself of just prior to these problems?
Most often when you have a plethora of problems such as you describe it is least time consuming and more apt of success to bit the bullet and re-install the OD and the applications you use.
Hopefully you have been backing up your data files that you need and can't afford to loose, but if not take some time to copy all your data files (and that includes documents, pictures and music, and etc.) to a flash drive or burn them to CD or DVD prior to a complete re-installation..
Depending on your computer's manufacturer and model you may be able to run a complete restore of the PC to factory specs from the restoration partition on the hard drive. If not be sure to check the manufacturer's site and download all the necessary drivers for yout specific PC.