The autorun.inf was a good suggestion, but it wouldn't be on your C: drive if its affecting your G: drive, so check the root of G:
One possible solution.
Check in the root of C: for a file named autorun.inf (you probably want to make sure you have your folder options set to show hidden and system files.) If found, rename it to disguise it, reboot, and see if things work better.
Something like this could potentially be caused by a virus so I suggest you scan your PC for viruses as well.
Edit
See the post below.
The autorun.inf was a good suggestion, but it wouldn't be on your C: drive if its affecting your G: drive, so check the root of G:
Also, not really a fix as such, but you can right click on My Computer, click Manage, Access the disk service and change the drive letter. Just to see if this has any effect.