Hello HomerJ,
this can be a standard issue that occurs when the services for ALM aren't running. Those issue could stem from anything such as a restart of the server caused a timing issue and the services attempting to start prior to the DB being made available (it needs to be up and running prior to ALM services being able to start), or something as simple as the server being down or the services just stopped. I would suggest seeing some of these other posts if staring the services doesn't correct the situation because as you can see it is a pretty common error:

https://eyeontesting.com/questions/11899/service-unavailable-message-in-browser.html

https://eyeontesting.com/questions/8323/our-alm-instance-is-down.html

https://eyeontesting.com/questions/16182/getting-alm-http-error-503-for-oracle-database-in.html

https://eyeontesting.com/questions/11371/how-do-we-stop-getting-this-http-error-503.html

I hope this helps,
Dan