This happened to me once, too. Not aware at the time of what was going on, I bought a Win 7 Pro key on eBay for $20. After only a month, my OS was flagged as being non-genuine, fortunately I was still under PayPal's 45 days of protection.
Although the seller was long gone, I got my money back. But I consider myself to be one of the "lucky ones", like TM stated, some runs OK for months, then goes black on you. Once your protection limit is up (usually 45 to 90 days, depending on the card issuer), you're screwed. There's no need to sugar coat it, that's the way it is.
For that reason, avoid sites like eBay (and other online auction sites) like a plague when buying software, especially watch for those who are only "key sellers", this is illegal, except as specified by Microsoft (when making purchases from the Microsoft Store or other sites that MS deems appropriate). Avoid street vendors also, as sure as fire, the copy is hot as hell. Even if it isn't at first, it will be later.
Some keys, like the Windows Anytime Upgrade, or a key to unlock any Office software that's preinstalled on your computer, can be purchased from MS Store (online or by phone), upon payment, the proper key will be emailed (or mailed in an envelope) to you. Then, you can type in the key from the proper place in the Start Menu to activate the product.
I realize that you're young, there's lessons to be learned, and one is to buy software only from authorized sources. I'm sure that there's places in your country to do things the right way, MS is a corporation that operates worldwide, as they want their customers to be legal.
If you cannot get this straightened out, and cannot afford a Windows 7 OS, then there's free options with Linux which will get you back onto the net, legally. Ubuntu is the most popular Linux OS, and one of the most user friendly ones to use. I use a variant of it myself in Mint, dual booting with Win 7.
I don't openly push Linux on this forum, for obvious reasons. But I'd rather see a user be legal, and not have to look over their shoulder, than to advocate piracy. Piracy, much like shoplifting, makes all of us genuine users pay more for our software. As high as prices are across the board for everything that we buy (food, gas, clothes, health care, etc.), these type of actions leaves us with even less to pay for our software.
If by chance you did buy this OS from a retailer, then you need to return it, if a reinstall, and reentering the proper key doesn't work.
I hope that you get this solved, so that you can have a legal Win 7, the way it should be.
Best of Luck,
Cat
