Hello and welcome to the forum.
It would be nice to have some system specs in your forum profile to be able to make a more educated guess Link Removed
But since your suspicions are probably pretty close, when the problem occurs can you enter the System's BIOS Setup Utility and check the Date and Time that it is reporting and check to see if it is accurate.
Sometime a bad capacitor (often in the Power Supply Unit) can drain the CMOS battery overnight and result in the system BIOS parameters defaulting to erroneous defaults.
Regards
Randy