Not able to download and open Facebook or yahoo

Hi I'm looking for some help as my windows vista laptop isn't downloading or letting me go onto Facebook or yahoo? I took of my avg as I was told it was making my laptop run slow, stupid I know. So now I think I have virus's that are preventing me downloading the files. I have also tried a free anti virus off a memory stick and it just tells me no room on the disk? I've tried deleting files, that hasn't helped. Any suggestions pks? I'm not the best with computers, so you may need it literally spoon fed to me so i understand lol. Thanks hannah