Good malware,spy and viruse terminator?

hey y'all,my computer seems to be infected with some kinda trojans,malwares and viruses but i can't find them and remove them.i used many kinds of Antiviruses and Antispies but none of them worked.the sign of this viruses and malware are,after about 2 or 3 days that i install the new window i can't access some websites like google,yahoo,isohunt,..... and every time i start IE7 an additional page opens up and tells me that my computer is infected with some viruses and malwares and i have to download the software that it offers me.it it's self sounds like a virus!!i used Kaspersky,Avast,Nod32,Spyware terminator,Norton but none of them worked well for me.if you guys have any suggestion about how can i survive this ultimate suffer! i'd be really glad to hear that.also i'm not in situation to afford format my whole hard disk.thanks.