Why my Nokia e61 restart itself?

I used a charger of an old 5510 to charge my old Nokia e61 when I was visiting a friend for some days and forgotten mine. Nothing happened this happens to some phones due to full memory or other memory problems.

Well, a loss of data may not be prevented. You should try formatting it. How is explained in the Most common problems thread at the top of this forum.

Probably there can be booting problem try logging in safe mode or you can try a new battery.

You can also try taking out the battery and memory card and then re insert them both and start the phone.