Nokia 3110c restarts automatic

Hello,

dear sir,
i have a nokia 3110 c phone and I use to send group msgs on it but because of some problem it restarts automatically so I took it to the mobile repairing shop where new software 07.21is installed in it but the problem is not solved so I want to update it manually through nokia software updater through pc but it displays you have latest software ie you are updated so please tell me the solution of this problem and is there any procedure of installing previous version of software into my mobile through pc through pc suit
so please send me the details of this problem
thanxxx