I forgot security code for k610i. IMEI 35170901-327361-1-69. I can't use my phone at all

You may try by following instructions given below.
Warning: Do not enter any wrong unlock unlock codes on your Sony Ericsson K610i mobile phones. If you enter over a certain amount of wrong unlock codes on your mobile phone, your phone may get hard locked and sometimes become unusable.

1 - Switch ON your Sony Ericsson K610i mobile phone without any SIM Card,
2 - Press the left arrow key/button once,
3 - Press the button * twice,
4 - Press the left arrow key/button once,
5 - The message "Personalize with MNC2" will appear,
(or you will have displayed an unlock menu, select the lock you want to unlock)
6 - Enter the Unlock Code.

If your Sony Ericsson K610i mobile phone does not have a left arrow button/key(e.g. Sony Ericsson W950i) and on a few phones(not all) that have a "JOGDIAL" you must press the "down arrow" key/button instead of the "left arrow" key/button for step 2 & 4. We mean by "Down Arrow" to direct the Jogdial down! In the Sony Ericsson W950i and some other models, the down arrow button/key would be located on the side of the phone.