I just checked back to add my OS, so thanks for the very fast reply!
I have Vista SP2 and haven’t used anything except for Windows Firewall. Avast is the only security software that’s always running besides the firewall. It’s on one of two home computers that are hardwired to a router (with no software program). I also scan with Malwarebytes.

I click the red x icon in the system tray to go to windows security center where it says windows firewall is not running. I click turn on now and get
Security center can’t turn on windows firewall
Turn on windows firewall manually

I click that and get to windows firewall and get the following message. (I made a mistake in my first post, it should be that the associated service is NOT running.)

‘Windows firewall settings cannot be displayed because the associated service is not running. Do you want to start the windows firewall service?’ Then I get a popup saying ‘windows cannot start the windows firewall service’ and that’s all. Same if I click ‘allow a program through windows firewall’.

The only different behaviour that’s happened is the avast program update.

Edit: I found these in the management console, order from most recent-

error- The Windows Firewall service terminated with service-specific error 5 (0x5).
info- The Windows Firewall service entered the stopped state.
info-The WinHTTP Web Proxy Auto-Discovery Service service entered the stopped state.
warning- Windows Defender Real-Time Protection agent has detected changes

I’m going to do a system restore. I expect that I’ll have to try upgrading Avast again after.

Update - system restore fixed it. Avast took a while to get going and allow connecting to the net but both it and windows firewall seem to be working fine now. As I was doing the system restore I saw that I had uninstalled Arcsoft total media software just after updating avast. Now I’ll have to uninstall it again and see what happens, but it doesn’t seem to be a problem with Avast. Problem solved, but thanks again for your quick reply.

Another update - the firewall problem isn’t solved. It was working until I uninstalled arcsoft total theatre for the second time after system restore. The computer shut down after uninstall completed, which it isn’t supposed to do. Today after bootup the exact same issues with the firewall are happening. Feeling vulnerable, I installed Zonealarm free firewall which seems to be working ok but I didn’t want to have to add more software. But it’s clear that Avast didn’t cause the problem. Now I want to find out why uninstalling that program caused these problems and how I can restore windows firewall and get rid of zonealarm.