From the comments:
Yes there is a red exclamation in the event log. This is the log "The
Windows Firewall service terminated with service-specific error The
data is invalid.." As you can see the log is unhelpful.
Actually, the event log is very helpful. It tells us your firewall data became corrupted.
You didn't specify the exact EventID but you could try resetting the firewall with the following:
Open a administrator prompt.
(Click Start, type
cmd.exe and choose
Run as administrator.)
Copy and paste the following command (and press Enter):
Rundll32 setupapi,InstallHinfSection Ndi-Steelhead 132 %windir%\inf\netrass.inf
If that doesn't work there is also the option (found in that second link) of running the "services repair tool by ESET" from here.
If both methods don't work please provide the exact EventId and text (like in this topic) so we can search more precise for a solution.