trouble scrolling

I seemed to develop this problem about 2 weeks ago the first time I enter a thread all works good then when I leave and go back in later it goes to the last post I read and I cant scroll up or down I done virus scans and the sorts all seems clean . is there a setting that I hit by mistake ?it seems to only happen here but that does not mean its the site it is most likely my pc . it sure does suck tho trying to follow threads . any thought's are welcome .