My guess is you’ve got something running in the background that loads on Startup, which the Task Manager doesn’t address.
Assuming you have some form of Windows?
Proceed with EXTREME CAUTION here.
Click on Start, then Run, then type msconfig in the Open prompt, and it will bring up the System Configuration Utility. Go to the tab marked Startup and peruse it carefully. My bet would be that down towards the bottom of the list there’s something RAM-hungry that is booting itself up and running in the background when you turn your computer on.
What you do is, you unclick it. Now, unclicking it won’t uninstall it from your computer, but it will keep it from running.
Where the “extreme caution” comes in is if you unclick the wrong thing in this Startup menu, your computer won’t run at all, so don’t go hogwild and start unclicking stuff unless you’re absolutely sure what it is.
You could Copy and Paste a list of what’s on there for us to look at and help you figure out what’s running.