You could try this program from Sophos to try and remove your rootkits http://www.sophos.com/en-us/products/free-tools/sophos-anti-rootkit.aspx
As well as scanning daily for viruses with AVG free (this can be set up to work automatically if you haven't already done this), you also need to manually use the AVG scanner for rootkits, perhaps once each week.
Do you also have malware removal programs installed, such as Spywareblaster and Antisuperspyware? These can both be downloaded from Filehippo http://www.filehippo.com/software/antimalware/. Spywareblaster works in the backgound when your PC is on and Superantispyware needs to be used to scan your PC weekly.