Need Help With Trojan (Believe to be Trojan.Virantix.b)

I am having a problem with a constant pop up showing "your computer is infected! windows has detected spyware infection!..." and on and on the warning goes. but i know this is a bogus warning.

i have symnatec anti virus running and it manages to quarantine the trojan.virantix.b file but it just starts up again when i log back onto windows.
i also notice that i have braviax.exe in the log below.

i'd love to know what to do.

here is a copy of my hijackthis log:

 

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