I bought Win 7 on ebay and now after 5 months my key nows says it is blocked. After doing some digging it looks like the product id is from a MSDN account. So, I was scammed. Anyway my question is if I buy an oem copy from newegg can I just change the key or do I have to reinstall? What about keys from technet? I could just join that and get a new key an some other software for not much more. I just don't want to reinstall everything.
Technet product keys are technically classed as being a form of retail key. I suspect that the same is true of product keys generated from MSDN accounts.
You generally can't use a retail product key to install from OEM media. The opposite is also true - an OEM product key cannot be used to install from retail media.
In your case, you have the equivalent of an OS install from retail media. Thus, an OEM product key will not work with it unless you do a reinstall of the OS from the OEM disc you buy. A Technet key could probably work (as it is a form of retail key), but you run the risk of putting yourself back in the same boat unless you actually purchase a Technet account.
I can tell you from experience Technet is a good deal as long as you use it for what it was intended and don't go giving away or selling keys. I'm not going to get involved in the "allowed" vs "not allowed" debate - I use it for what I use it for, and that is that. Microsoft comes out ahead because the now get a yearly payment from me whereas I only used to send them a little money every 4 or 5 years for an OS upgrade (and it had been awhile considering I skipped Vista). Some people buy an account just to get the product keys and then let it lapse. I keep mine active.
Some folks argue they are loosing out on a sale of their other products to which I have access (like Office, or Windows Home Server, for instance). However, they really aren't because in the past I would never have wasted my money purchasing any of that software when there are good free alternatives like OpenOffice. And, I already have cheap access to MS Office through my employer's Home Use Program agreement anyway if I want it.