BIZMAN HELP 
Alright, what Gyrene said about formatting and reinstalling is sound advice.
However, you might get satisfactory results with some tricks. Caution: It'll take half a day at least.
Since you said it's some kind of adware, I'd start with adware specific cleaners.
Malwarebytes' AntiMalware has been one of the best, free for home users.
SuperAntiSpyware free or portable is another great one.
Eset Online Scanner is quite effective against both viruses and other "possibly unwanted programs". Remember to click the Advanced options link and tick both the potentially unwanted and unsafe applications.
Many adware applications reside in temp folders, so cleaning them is not a bad idea.
Ccleaner is a great tool doing that. If you start with it, the scanning times with the programs above may shorten, but psychologically you might want to search for adware also in the temporary folders - and find some there.
If the above doesn't help, try
ComboFix. There's a thorough
Usage Guide for it, advising you to send the report for further investigation, but as it says,
It is possible that ComboFix, even on its first run, may have fixed the problems you are having
. In difficult cases I've started with ComboFix, then run the above mentioned which mostly clean what's left.
Again, as said, the only 100% solution is to wipe the hdd and reinstall from scratch. A cleaning may give the same result, but it might as well leave residues which may reactivate. Be cautious when using a cleaned machine.
And as Olds said, get an active anti-virus and run it. Avast and AVG are good choices from the free ones. Also check that you're behind some kind of a firewall. Your modem might have one, Windows sure has one.
