tried to access a few different sites and a certificate error pops up, help?

[999]

I have been trying to access Pinterest on my vista pc and it pops up with SSL error 'This sites security certificate is not trusted' when i click proceed anyway the website shows like its a broken site, and it won't let me log in, i know pinterest is a okay site to use, and it works fine on my windows 7 laptop, i have looked on a few sites for help all they say is change date & time settings to correct date & time and my date & time is already set correctly but i set it again anyway, that doesn't work, clearing cookies/caches, that doesn't work either, also tried using internet explorer rather than google chrome and the same thing happens, please help?

[DunbarPappy®ϟϟ]

Most common fix:
Right click tray time> "Adjust..."> Update.
While here, tick 'Automatic synchronize...'

Another situation:
"On board" browser certificates not current.
Vista/Win7: Go to your "Windows update" in Control Panel> follow prompts.