It's not a firewall, but you might find that Avast Antivirus helps you get things cleaned up at least.
It's a free one, and assuming none of the virii you have are changing URL's to dodgy sites you should be able to download it from
http://www.avast.com/free-antivirus-download - as a check, that url should say avast dot com free dash antivirus dash download.
What firewall were you using? If it went down without warning I'm not so certain it expired - those things normally give you a month or so of "Your subscription to ExpensiveFirewall will expire in X days. To avoid interruption to service, renew your subscription." windows that have to be closed before you can get on with anything else.
My best guess is a bit of ransomware has disabled the firewall or even just started claiming that the firewall has expired in an attempt to trick you into paying for their dodgy service.