I have a virus on. I have a virus on my laptop and can not get past XP2008 anti virus software

Question

I have a virus on my laptop and can not get past XP2008 anti virus software without them wanting me to buy it. I have downloaded AVG virus free software and tried to run it on my laptop but it will not load I get the error message:- Action failed for file avgwdsvc.exe : starting service Error 0x800736b1. Any computer buffs out there with a clue how to get around it. Thanks. Tom email [e-mail]