I have a dual booted laptop with windows and ubuntu installed side by side. whenever I boot in to any one these operating systems, the system clock shows the time I booted in the said OS last time. For example, If I boot up windows OS , do my work and shut it down at suppose 8pm, then I open ubuntu do my work shut down ubuntu. now next Time I boot in to windows it is still 8pm the system clock time is never updated automatically according to real-time . In fact I have to go in to date and time settings every time and set it manually. This happens with ubuntu also(i.e system clock never shows real time but the time I shut it down at) . why don't system clock time updates itself automatically?
As has been mentioned, the CMOS backup battery on your motherboard is possibly the problem.
They usually take a CR2032 cell battery which costs very little (less than $1 probably). You should be able to get them from most hardware stores.
Just buy one, pop open your PC case, and swap it out on the mainboard. It's very likely to be the issue if your PC is either a few years old, or has been stored with the power off for some time.
Here's how to do it: [https://www.youtube.com/watch?v=AkNXDRUfWoU]