System reserved partition becoming "visible" and intermittently assigned drive letter by Windows

Hi,
My windows 7 is suddenly applying a drive letter to the system partition, and removing the letter which causes the "new disk inserted" window to keep popping up every half second. In Disk Manager the drive letter appears and disappears every half second.
The only way I've stopped it is to permanently apply a drive letter, which means it is now visible in windows explorer.

I assume by 'system partition' you really mean the hidden system restore partition installed by your PC builder? If so, then after I just fired up Paragon Partition Manager to see what it makes of that partition on my Win 7 PC, I find the partition is Primary, NTFS, active, not hidden, volume name WinRe.

The main interesting thing is the volume letter seems to be set to '*'. It appears as (*) rather than (C: ) as the OS drive does. Furthermore, the main menu has a 'partition' tab, where one of the options is 'assign drive letter', and the next option below is 'remove drive letter' which is currently greyed out.

Looking at the standard Windows computer management, storage, disk management, I see a similar picture, except there is no volume letter at all (apparent in that window anyway).

Quite how the partition gets identified in that way is a puzzle, but you might try a free partition manager, such as gparted and see what that says, and possibly allows you to change. As I say above, Paragon Partition Manager might let you de-assign a drive letter but I dont dare try it myself

The partition is the "System reserved" partition that is created by Windows 7 installation!!

Yes, thats it, that's what WinRe probably means as a volume name.....not Windows Restore, but Windows Reserved ? Either way, try a third-party partition manager to de-assign a letter.