Look in Control Panel > System > Device manager and see if there is yellow question mark or exclamation mark anywhere.
If you find one it will probably relate to something lacking a proper driver or device without a driver.
If no warning signs then...........
It is also possible that something is trying, or scheduled to run and you haven't noticed.
Try Start, > Run, > MSCONFIG and pick the Start tab. You should see listed all the programs that start when you do.
Unless you have special reason, stay with just 4 and clear the ticked boxes of the others.
The 4 you should leave are
LoadPowerProfile ..... there should be 2 of these.