Time.windows.com

If the time doesn't change from one day to another, it's likely that the motherboard battery is starting to wear out, and you should consider changing it.
The battery is generally a button cell located on the motherboard that can usually be replaced easily.

When I click on the clock, it doesn't give me the option to modify
What should I do please?

Disable your firewall and update.

I have a problem with Windows Update (on Vista).
You'll tell me "this has nothing to do with the subject!"
Yes. But no.
After some research, I came across the issue with the 'time' function of Vista... And my computer is no longer synchronized with time.windows.com... Who knows why?
And because my clock resets every time I start my computer, and Windows Update needs my computer's time to work, well, it doesn't work anymore. Could someone help me?
Thank you in advance

I didn't say anything, I found it!
When you start your computer and have to re-set the time, do you think about the date? If so, have you thought about the year???
Since I set the year, everything is working perfectly... Good luck to you!

Sorry, but the speaking clock site is no longer accessible since a while.

Thank you Zozonno, you solved my problem :)