If eNB or MME failed to start you should check their output, the most probable causes of eNB or MME failing are:

• License issues: wrong license, no license, license doesn't support a specific feature, etc...
• Configuration syntax error

Press ctrl + a then send 0 to switch to [0 MME] window.

 To verify the 4G/5G service, you can do

(mme) enb # or gnb if running 5G

Press ctrl + a then send 1 to switch to [1 ENB] window.

[1 ENB] window lists some necessary parameter, such as 

RF0: sample_rate=23.040 MHz dl_freq=2600.000 MHz ul_freq=2600.000 MHz (band 38) dl_ant=2 ul_ant=2

To obtain the setting of TX/RX gain, you can do:

(enb) tx_gain
(enb) rx_gain

To adjust the gain temporarily, you can do: 

(enb) rx_gain 60
(enb) rx_gain
Chan Port Gain(dB)
 RX0    0     60.0
 RX1    0     60.0
(enb) tx_gain 50
(enb) tx_gain
Chan Port Gain(dB)
 RX0    0     50.0
 RX1    0     50.0

To verify UE connection, you can just input:

(enb) ue

To interpret eNB logs, it is important to understand the different steps for an UE to connect to an eNB:

• S1AP connection: connection between eNB and MME, this happens inside the ORS in software
• PRACH (Physical Random Access Channel) signal: sent once radio link is detected
• RRC (Radio Ressource Control): setup connection to transport NAS messages
• NAS (Non Access Stratum): messages between UE and MME

Here is what to do depending on what you see in the logs:

• S1AP connection fails: mme_addr is wrong
• no PRACH signal: either the frequency configuration is wrong, your UE doesn't support the right frequency or ORS signal doesn't reach at all the UE (ORS and UE are too far apart or gain is too low). Without PRACH signal, the debugging cannot go much further. 
• PRACH signal but not RRC: the radio link probably has bad quality, you should try increasing or reducing TX gain.
• NAS messages: SIM card configuration or APN configuration is wrong, or the wrong SIM card is used, or radio link has bad quality

At the beginning of the log, you will find some useful parameters: 

# SMP C=2 bandwidth=40.0/480 PRACH=1 DRBs=1 RF0=1/1
# Log file format:
# time layer dir ue_id {cell_id rnti sfn channel:} message
# Cell 0x01: earfcn=38050 pci=1 mode=TDD uldl_config=2 sp_config=7
# DL: n_rb_dl=100 cyclic_prefix=0
# UL: n_rb_ul=100 cyclic_prefix=0 prach_config_index=4 prach_freq_offset=11 delta_pucch_shift=2 n_rb_cqi=1 n_cs_an=0
# PUCCH allocation:
# Type     RBs    n
# 2/2a/2b    1    6
# Start of PUCCH ACK/NACK=11
# RBs reserved for PUCCH:  0  0 22  0  0  0  0 22  0  0
# SR resource count=44
# CQI resource count=48
# SRS resources: offsets=16 freqs=20 total=640
# GBR limits: DL=7.124 Mre/s UL=1.797 Mre/s