3510i data cable makes the on/off switch unavailable

Hi,
little problem...... I bought a MA-7660 data cable to link my phone through
a serial port to my pc.
Worked several times very good, made backups, installed new games.....
One time during transmitting my phone went dead. I thought it was the on/off
switch that broke down.
Since I still had warranty on the phone, I returned it to have it fixed. I
got a replacement-phone.
Uploaded my phonebook, games.... Worked fine.
Then my phone came back repaired.On/off seemed to be working.
So I reconnected to upload my backup, phone went dead again.
Angry I got back to the store and complained that the problem was not fixed.
Same story, replacementphone... come home, connect to pc,
.........replacementphone went also dead.
The screen flickers for one second, and switches back off. Now I have no
phone that works, and a lot off trouble
when at the store they'lle find out it's not the on/off switch that's
broken, but that it is my fault using a data-cable.
Is there not a reset button that I can push to repair the replacement phone
?
HELP PLEASE !!
Gigibros