As Windows 7 has already been released officially, more and more net pals begin updating to Windows 7, but recently, many guys said that even when installing Windows 7 of valid version, the validation still has a problem: after entering valid serial numbers, it shows “Error code: 0XC004F061”, which makes many people blocked and have nothing to do with it.
  Actually the reason is because this serial number is of “update serial number”, which could only be used for “Update installation”, but not “brand new installation”. So such kind of problems mostly happens on the machines updating from XP to Windows 7.
  Here I searched some solutions for this kind of problem to share with you:
1. Omit to enter serial numbers when installing, or direct neglect it. System would prompt you that you have 30 days’ activation period;
2. After entering system, don’t do any update, directly open REGEDIT.EXE to change registry. Under the address HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/, change the value of the key MediaBootInstall  from 1 to 0, and then save;
3. Search cmd from Start menu, open it with administrator identity and then type slmgr /rearm, press Enter and then wait for confirmation dialog to appear.
4. Restart;
5. Enter the serial number again, then activation will prompt it successful;
Special attention: this method is only limited to the situation that you have the valid Windows 7 s