Have you replaced the UCSB (after swapping the flash memory card from the original UCSB into the new UCSB? Have you done any necessary configuration for the new UCSB in ToolboxST?
Can you ping the UCSB from a command prompt window on the HMI?
When did this problem start? After a download to the controller from TooboxST? After the UCSB was powered-down or lost power? When did this problem start?
Is the machine (turbine and driven device) running and this is one of two or three UCSBs that has suddenly, without being powered-down or losing power from its 28 VDC power supply, has gone to this state (BOOT LED flashing)?
Often this can be an indication the flash memory card has a problem. RTFM (Read The Fine Manual) about how to program a flash memory card using the provided flash memory "burner" device. There may even be something in the ToolboxST help about this. You can also consult the Mark* VIe System Guide, GEH-6721, in the UCSx section, for troubleshooting help with UCSx problems.
That's all I can offer based on the information provided. It's probably best to have a Mark* VIe knowledgeable/experienced technician come to site to help with the problem.
Appears like you have lost the program memory. I would prefer resetting the controller from a 4GB USB 2.0 (NOT 3.0) pen drive, followed by program might help.