Why anti-virus and fire wall both can't work on my laptop?

I ever download several kinds of anti-viruse and fire wall but both can't work on my pc.

I don't understand pc so who can help me how to do on my pc to solve it ?

Why anti-virus and fire wall both can't work on my laptop?antispam

Some antiviruses and firewalls will conflict with each other.

Why anti-virus and fire wall both can't work on my laptop?avast

download AVG free from www.avg.com it comes with its own firewall. Best anti on the net!!