Check out this link, I have a feeling this is what you are suffering from:
http://botcrawl.com/how-to-remove-text-enhance/
Note though, that those instructions may stop this adware from functioning, but you are still probably infected with other viruses/malware that were used to install the adware. That is why, after you managed to get rid of the ads the first time, they came back. So, you should still run multiple scans to get rid of any viruses or rootkits.
I’d suggest downloading MalwareBytes Anti-Malware, like others said, but also get TDSSKiller from Kapersky Labs and a utility called RKill, available at bleepingcomputer.com.
Restart your computer in Safe Mode with Networking Support. Then, run RKill first to stop any malware processes that still manage to run in safe mode. Next, run TDSSKiller to remove any rootkits. Then, run a full MalwareBytes scan and remove anything that it finds. Unless you’ve got a particularly bad virus, that should get the job done.
On top of all of Boogieman’s excellent suggestions, try running mrt.exe (Microsoft’s malicious software removal tool) from the run prompt. Also download Avast. Once Avast (free) is downloaded, run a boot scan. Avast’s boot scan often picks up things others miss. Do all of these processes in “Safe with Networking” mode. You may want to disable Norton, as it may interfere with Avast.