First, it would help if we knew more about your computer... Operating system? Make and model? Etc.

In the meantime, on a separate, "clean" computer, please visit the website below, review the instructions, and create Avira's Rescue Disc which you'll use to boot from and run scans BEFORE Windows loads.

http://forum.avira.com/wbb/index.php?page=Thread&threadID=82163

After you allow the Rescue CD to clean what it can, use the instructions below to run some other clean up tools... It might be best to download the tools on a separate clean computer as well.

If you can download the tools listed below on the problem computer, great, but you may need to use a separate, clean computer, download the tools, copy them to a DIFFERENT flash drive or CD, then transfer them to the infected computer.
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Once that's done, then restart the computer into "Safe Mode with Networking" and use the instructions below. If you can't start in Safe Mode, then run all the tools while in "normal" Windows first, then run them in Safe Mode afterward.:

After downloading or transferring it to the problem machine, run the
following tool to help allow the removal programs below to run.
(courtesy of Grinler at BleepingComputer.com)There are 3 different
versions. If one of them won't run then try to run the other one. Be
patient.... as a black window should open, then close after finding all
the background programs.Vista and Win7 users need to right click and choose Run as AdminYou only need to get one of them to run, not all of them.

Rkill.exe
http://download.bleepingcomputer.com/grinler/rkill.exe

Rkill.com
http://download.bleepingcomputer.com/grinler/rkill.com

Rkill.scr
http://download.bleepingcomputer.com/grinler/rkill.scr
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IMMEDIATELY after running the "Rkill" tool above, run/install the Malwarebytes and
SuperAntispyware installer and update files from the links below which
you've also copied to a CD or flash drive, and transfered to the problem
machine. Do NOT restart the computer after running Rkill.Once
downloaded and before transferring Malwarebytes and SuperAntispyware to
the problem machine, rename the program installer "mbam-setup.exe" file
to something else like "Gogetum.exe", then copy the installer file and
the update file to a CD or flash drive.. Transfer the file to the
problem machine, then install the "Gogetum.exe" file, then run the
update to get the program current.. After that, run a full system scan
and delete anything it finds.

Malwarebytes Installer Download Link (Clicking on the links below will immediately start the download dialogue window.)
http://www.besttechie.net/tools/mbam-setup.exe

Next, install and run a full system scan with the SuperAntispyware program
and the manual updater from the links below. As before, you may need to
rename the installer file to get the program to install.:

SuperAntispyware
http://www.superantispyware.com/SuperAntispyware

Manual Update
rhttp://www.superantispyware.com/definitions.html
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And after that, if everything's fine by you can't connect to the internet,
then follow the procedures below to check your network "proxy" settings
again.Open Internet Explorer and go to Tools-Internet
Options-Connection Tab. Click on the LAN settings button. IF there is a
check mark next to "Use a proxy server for your LAN", uncheck it. Click
OK. Then OK, again.
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Hope this helps.

Grif