Your system has a virus or other malware.
These are classical symptoms.
And it seems your own virusscanner can't catch it.
Installing another anti-virus product is probably not gong to help, because anything you do on an already compromised system is unreliable. This also applies to manually trying to disable the malware. There are multiple components of it installed but you can only remove 1 at a time, so the others can simply re-active the one you just killed.
Best thing to do is to scan and clean the harddisk from a clean state:
- Pull the harddisk out of the computer and hook it up to another (clean) computer as 2nd disk. Then scan the disk from the clean system. Use multiple anti-virus products if needed if the first doesn't find anything.
- Alternatively: Some anti-virus products have a live-USB stick solution. You boot from the USB stick (in stead of the compromised harddisk) and scan the infected disk using the software on the USB stick. Obviously you will need to download and make the USB stick on another clean system.
See also the link that RamHound just posted in the comments. I was going to link to that same question but he was faster than me.