Hello Christine. I'll post full details in a moment . .
I'd been too busy to get back on this because of having to resolve other MS failures and then when I was ready to post, MS screwed up again and I was one of the many whose profile was blocked.
So to explain. I previously had the Solitaire Collection on my bottom tool-bar - I clicked on it and played as a Guest - no problems until now. After following Catherine's very helpful suggestion re BITS, I was forced to sign up as a member and I now have a profile. The first time after that when I signed in it all went pear-shaped again. Various delays & problems - that's when I was about to tell Catherine. Since then, it's hit and miss - my workaround is to click on my icon and when it says "Signing you in" or whatever (as a member) I click on close/stop. That sometimes enables me to play as a guest and sometimes doesn't so I hope this extra info will enable Catherine to come up with another solution.
Catherine - this problem started around the 15th March, the day of a Failed Cumulative WU. That was successfully installed on the 16th. Could the failure have caused this problem?