Lots of trouble!!

I am having a lot of problums trying to down load any kind of viruse detection. It all started a few days ago. I got this thing that started scanning my files on my C drive and all others on my computer on the my computer page. said it found all these trogins and such to down load some virus protection programe. Now when ever i try to down load a Antivirus or hijack this i get all kinds of errors ranging from out of date java version go to java to download new one. I go and down load the latest and try to run the scan agine and get the same error. Or i get one that says not conpatable with my version of internet explorer. I have tried to down load hijackthis and it never down loads. I am running Windows vista home basic with IE 8 every thing is updated. Can any one help ?