I once had this problem with my 6230i when I created a lot of MMS's on the PC with Oxygen and then wrote it to the phone.
I expected it to give a write error at some stage because it was a lot of MMS's and I knew the phone did not have enough space for it. But it wrote everything. And then the phone was fully busted.
It would reboot a lot and when you entered the menu all the icons where question marks. Could not even reach the gallery.
My guess is that Oxygen wrote over into the reserved memory of the phone where the OS is and corrupted themes and other files. Perhaps the same happened to you by other means ?
I took it to my nearest nokia service centre and asked for a "firmware fix" because my phone was "unstable" - ya rite.
An hour later I had the newest firmware and my phone was as good as new ;-)