That is very likely a hardware problem. Issue with troubleshooting this is that you would need to wipe it and set it to factory default to see if that fixes it, which means internal memory will be erased. If you have files on the SD card, remove the card then do a factory reset on the device. If that does not work or if you really don't want to lose any files from it if you never backed them up, you'd need to bring it in to be looked at by your service provider. For an S2 it may be cheaper to just replace it than try to get it repaired.