performed an "operating system diagnostic" test via HP messages prompt, now not working correctly

[Titchy1]

hp Pavillion dv6-2111sa O.P. Windows 7. I am aware this is an old laptop but it serves me well for my needs. Last Sunday I was prompted by HP messages to perform a "Operating System Diagnostics" task. It completed the first 3 tasks with a green tick in the designated boxes but after 3 hours the final one was still going so I shut the box down and left the page. All seemed fine for the rest of the day, so logged off & shut down as usual. Next morning, logged on and nothing would load, most stuff had disappeared off bottom task bar. Managed to get some back (I'm not very techie at all) inc. date & time which read 31st.Dec. 2008!!! Typed in correct date & time but then had to wait ages for updates?? to load. Seemed ok for a few hours then noticed date & time had changed again to Aug.2009. Yesterday morning the same, so decided to do a restore. I only wanted to restore back to last week but the only date offered (apart from Sunday when it all kicked off) was Nov. 2019 and didn't really want to go back that far. Any thoughts on what has gone wrong?

[Lil_Boy_Blue]

Hi

The Time and Date are usually a CMOS/RTC battery thing.  A replacement is only a coupla quid.

https://www.techwalla.com/articles/how-to-check-the-cmos-battery

https://www.newegg.com/p/pl?d=cmos+battery

If in doubt please ask.