macbook date and time set to 1 January 2015

Hi, on my macbook air (Yosemite), yesterday the date reverted back to 1st January 2015. The battery was low, the power cable was plugged in, however during booting it switched off. Since then the date and time are incorrect. Today it's the 2nd January 2015, so it does increment, but do not update to the current date.

Additionally all the certificates are unverified. Whenever i open a website i get the message that the certificate is not verified and asks me to continue or cancel.

I'm also no longer able to connect to my apple-id.

I presume that all these problems are related. The automatic time/date is active (time.euro.apple.com), however, date and time are not correct.

i just reinstalled the macbook, but the problems are the same.

any idea what the problem could be and how to fix it?

thanks!

ciao

marco