Text freezing motorola v550

Once I wish to type a text message my phone allows plus/minus 3 to 5 characters before the entire phone freezes up therefore I have to remove the battery from the phone to switch off and reenter my pin number to reactivate.I can receive and make calls but text function outgoing is a definite no no.It appears that not even master reset will resolve this problem.I was advised by a fundi that I have a cellphone virus,yet I do not use my phone for anything else apart from text messages and making/receiving calls.Where to from here.

Great .... it helps alot... sobra!! thanks..(salamat) :)

Motorola phone freez in txt massages
press menu
select setting
go to initial set-up
MASTER CLEAR your phone
your phone ask for your security code
the deafault of security code of motorola is (000000)
but some people change it.
enter your security code. and select ok/yes.
take note: your phone file will be lost'
such as pics., tones, and videos.
after master clear done..
do the same procedure
and select the MASTER RESET.

How do i open a security code that cant remember