If your Start page is constantly being changed, or some unknown sites are opening, follow the given steps:
1. Download file http://www.virusinfo.info/soft/ie_reset_defoults.zip, unpack it and run the REG file inside. It is the simplest way, and it rarely helps, but it is a good idea to try it.
If the file doesn't help:
2. Install some antivirus software, update the database and do a scan in Safe Mode.
If the problem persists:
1. Download HijackThis http://www.trendsecure.com/portal/en...hijackthis.php
2. Do a scan in normal mode, do not fix anything.
3. Save the log.
4. Go to http://virusinfo.info/showthread.php?t=9184. Open a new thread, give it a name describing your problem, and attach the HJT log.