Samsung Galaxy S + reboot problem

[guest]

I have a problem with my galaxy s +. It does a weird reboot thing at random times. It starts up and the start up animation starts however I do hear the start up music nor do I need to enter my pin. I also have the problem that after this, I do not have internet through 3G. To fix this, I usually reboot or go into airplane mode and exit it. This is quite annoying and I want this to stop. Does anyone know how to stop this?

Thanks in advance.

[guest]

Factory reset and clear cache will probably resolve it.

[guest]

The reset hasn't helped. Don't know how to clear the cache though.

[guest]

Factory reset and Clear cache through Recovery mode.
Press and hold volume up + Home button + Power button until in Recovery Menu with blue writing.