I can't boot into recovery after I flashed UD2.3
Can someone help me please.
when this happens to me, as it does occasionally regardless of which rom I'm using, I just open Rom Manager and reflash Clockwork (assuming that is the recovery you are using) until I get the notification of a successful install within 3-5 seconds of starting the reflash. Sometimes this will take many (5-10) tries before it gets there. Once I can get the notification back fairly quickly Clockwork then works for me.
Another issue you may encounter is the phone rebooting spontaneously while in Clockwork. If that happens just immediately press and hold the X key and the phone will reboot into Clockwork. I've never had Clockwork cause the phone to reboot a second time.
Good luck.