You must have uninstalled your graphics driver.
Go here:
http://www.nvidia.com/Download/Scan.aspx?lang=en-us
Allow the Java applet to run an automatic graphics driver detection, and install the driver it recommends.
Anyway, if the processor is under 100% load without you knowing what does it do, this indicates some sort of malware infection. You should
- inspect the running processes to find out, what might cause the load
http://en.wikipedia.org/wiki/Windows_Task_Manager
- if necessary, run antivirus/antimalware scans
http://www.malwarebytes.org/
- alternatively, you can back up your personal files, and restore the factory setup, if the feature is available on your computer/you have the restoration disks. (Of course you could do a complete operating system reinstallation too, if you have an install disk.)