Its changing things for me?!

Hey guys. Your my last resort for help! my internet was running really slowly so i thought i'd run some antivirus software and such, and it seems to have unearthed the depths of hell!? main problem being that now i seem to have no 'turn off computer' button in my start menu, or a 'run' button either. 'Ctrl Alt Del' brings up an error message of 'task manager has been disabled by your administrator' but im the only one on the computer and there are no other accounts, and, probably the weirdest one which, in the light of things made me laugh as it was what i was thinking at the time, if i go to 'log off' which is in my start menu, instead of being greated with a nice 'Turn off Computer'.. i get have to click a line reading 'Turn off Pain In The Butt' .. ?!?!? im guessing this is a virus or malware or something, but have no idea how to get rid of it? also my pop ups seem to have got worse lately so maybe its some adware? im running AVG antivirus and anti spyware.. they've cleaned the best of it out but i need help getting my buttons back! lol. please help if you can! thanks again. Shadow