i have a nasty virus on my computer PLEASE HELP

i dont have a clue what is going on with my computer. it is runinng 10 times slower, internet explorer is crashing every 2 minutes, i cant open the task manager ( i typed taskmgr in start\run but it says another program is using this file). i have runned nod, ad aware and deleted all threats. i downloaded smitfraudfix and i have the same problem as with the task manager. When i used the ad aware i noticed that it was scanning a folder that i cant even see (it turned on the hidden files option in the folder options) that is full of movies, music and porn files. i dont know how to find it and delete it.

Please, does anybody know any solution?