2004 Jeep TJ Possible clutch/transmission problems

Hello I have an issue with my Jeep TJ not going into gear properly. When trying to shift into gear from a stop I can hear a squeaking/slight grinding sound and will not go into gear. This only happens when motor is running, while the ignition is off I can shift into any gear without issue. Clutch pedal feels the same as always and I have not noticed any signs of the clutch slipping. This problem started without any warning at all, one minute everything is fine and the next it will not go into any gear. I have checked the slave cylinder and lines they look fine. Transmission fluid is fine. I am contemplating purchasing and installing a clutch kit but am worried that my problem might be the syncro's. Any help you could offer would be greatly appreciated.