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

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