my friend send me a trojan through an email attachment and now i gota trojan in my pc....aint that some sh1t........now i cant reinstall my mcafee virus scanner.....what can i do to fix this huge problem......please help....

i installed the virus scanner and it deleted the trojan....but when i try to re install it it does not let me....it says an error that the intallation failed even do mcafee seems to work..i'm confused right now....some1 please help