OK. Can’t say I know much about that model, but I was going to recommend doing a reset. Be warned though that you will probably lose all of the contact information off the phone, so stick your friend’s SIM card into it so you can switch it on, then write down any info you don’t want to lose.
Now for the reset (shouldn’t affect your friend’s SIM card, but maybe writing down THEIR numbers might be a good idea… you know… just in case.)
I can’t find a manual for your phone on-line (In English) but if you have one, try to find out how to reset the phone. It’s usually somewhere in the settings. In my experience, there are usually two types of reset. One is more of a reboot, whereas one is more of a back-to-factory-settings thing. The first one should be tried first, as it usually doesn’t delete anything. If it doesn’t work, then try the second. In Motorola phones, for example, these are called Master Reset and Master Clear (respectively).
If you have any doubts about which option to choose on your phone, feel free to ask. I can give you an educated guess.