You have a malware infection, use the following free programs, download, install, update and reboot into Safe Mode to scan:
Remove Restrictions Tool:
http://www.softpedia.com/progDownload/RRT-Remove-Ristrictions-Tool-Download-68926.html
Download from Softpedia Secure Download (RO), install, run and check all boxes then click Apply and then reboot. This tool re-enables what codecs/viruses have disabled.
Wallpaper Hijacker Removal Tool:
http://www.majorgeeks.com/Wallpaper_Hijack_Remover_d4816.html
Note: You should hit all "Repair" buttons even though it may not say "Found!" This will fix a wallpaper hijack everytime if all repair buttons are pressed.
Malwarebytes Anti-Malware:
http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?hhTest=1.
Download, install, update and select Full Scan.
Remove all infections that it finds after scan.
SUPERAntiSpyware Free Edition:
http://www.download.com/SUPERAntiSpyware-Free-Edition/3000-8022_4-10523889.html
Download, install, check for updates, then select Scan your Computer, select your drive and select Perform Complete Scan
Spybot S&D:
http://www.safer-networking.org/en/download/index.html
Download, install, update and Immunize, turn off Tea Timer then click 'Check for problems' then when complete select all and then 'Fix Checked'
Open Spybot, click on Mode, select Advanced, click on Tools then Resident and untick Resident 'Tea Timer'
Do NOT untick Resident 'SD Helper' as that is your protection.
Spyware Doctor Free Basic Edition - Realtime monitoring:
http://pack.google.com/intl/en/pack_installer_new.html?hl=en&gl=us&ciNum=12
Its free with Google pack, untick all boxes except Spyware Doctor. Download install, update and run.
SmitFraud Removal:
Firstly, download the removal tool from here:
http://siri.geekstogo.com/SmitfraudFix.php
Then follow the instructions on the page
ONLY IF the problem persists, turn OFF System Restore, Right click My computer > select Properties > System Restore Tab > Tick Turn Off System restore on all drives.
After scans are complete and machine is clean remember to turn system restore back ON and create a new restore point.