You can try a couple of things:
- Hard reset: (power off the phone) then press and hold the vol down and enter buttons > soft rest and then very quickly press the power button. This can be tricky and you will most likely have to try a few time.
- Load another ROM via the SD card: copy the ROM NBH file from RUU_Signed.nbh and rename it to RAPHIMG.nbh
It sounds like you make have just loaded a bad ROM. Hope this help and you can take a look here for more details:
http://forum.ppcgeeks.com/showthread.php?t=43266