It's not asking you to upgrade - it's asking you to register the copy of windows your machine is running (this is a user-license requirement). One of three things has happened:
1. You bought the machine new and failed to follow the instructions to activate the operating system on first use
2. You bought the machine "pre-owned" and it has an illegal copy of Windows on it which is already registered elsewhere
3. Your system has become corrupted and *thinks* the activation hasn't occured.
If it's (1) just go to settings and activate the software (it's free).
If it's (2) then you'll have to buy a legal copy of Windows and install/activate it
If it's (3) you need to contact microsoft's on-line help facilities and they will assist you in diagnosing/fixing the problem
Actually there is a (4) - if you have changed the disk, the motherboard or the processor of the machine it may need you to re-activate it by talking to microsoft. This is a facility to stop people copying an activated installation onto multiple machines to avoid paying for the software. I don't think this will be the case because you said this had been happening "since day 1".
Does that help?
PDR