Windows 7 Activation Problem

[raj2007]

Upgraded my PCFrom - Intel Dual core 2.6, 2 GB RAM, Win 7 32 bitTo - Intel i5 3rd Gen Quad core, 8 GB RAM, Win 7 64 bitI used a win 7 64 bit Genuine product key which was lying unused for nearly 2 yrs..:stupid:. I installed it on Sunday evening. On Monday morning my desktop went black displaying "This copy of windows is not genuine". I re-entered the key and till now(TUE morning) no issues. Anyone faced this issue?