We sometimes hear from users of Series 60 handset users stating that they've
filled up their memory, and the memory is so full that they can't get in to
delete any files.
We've not had any experience of this, but the best thing to try is to
restart the phone (by taking the battery out) when it "hangs" and then
starting the phone in "safe mode". This causes the phone to load as few apps
as possible at startup. To do this, hold down the ABC key, and while holding
it down, start up the phone. Hopefully you will then be able to transfer
files from your C drive to your MMC to free up the memory.
As a very last resort, you can format the phone and start again - 1st post
in this FAQ section - This will remove all data, and you'll have to restore
your phone's information from a backup which you may have made on your MMC
or via PC Suite.
If you still can't get into the phone, the final option appears to to be to
take the phone to the nearest Club Nokia shop (or your retailer), who should
be able to re-flash the phone to factory settings.