Windows Vista IE will not let me download

Yesterday my computer just started wigging I could no longer get onto firefox. I tried downloading firefox again but IE would not let me download it in fact it will not let me download anything....plus it has gotten extremely slow...like really slow...i have cleaned it up and defragmented it. Now when I am typng it misses some of the keys i hit so have to go back and retype the missed key...what the heck is wrong...it was fine and till yesterday now it is all weird...please HELP

 

Probably best to read this and post followups to the malware and virus removal forum.