I bought Windows 7 Ultimate from eBay around 8 months back. I got original Microsoft DVDs (for 32 and 64 bit) product sheet. To verify the genuinness, I activated the windows immediately after installation. It got successfully activated.
After that, I used Microsoft's online genuine windows check and it was also successful. Everything was working fine since last month. Windows updates were regularly taking place. Then one fine day, I got blackground and a message telling me that my Windows is not genuine. I discussed with friends and they suggested to re-install it.
Today I re-installed the windows and tried to activate it. I gor the message
Your Windows Product Key is blocked by the activation server.
What is the solution for this problem? If my windows were nor genuine, how come it worked properly for around seven months? Shall I contact Microsoft for the same? I don't know where to contact Microsoft.