There is a couple things that will cause the Sparc 5 not to boot. One is if you have a missing or bad keyboard.
You can connect a hyperterminal (Windows PC COM1 or COM2) or another Sparc Station serial port "A" (using the tip command) through a Null Modem to the Serial Connector on the back of the UltraSparc 5. When you turn on your Sparc 5, you will be able to view POST (Power On Self Test). It may indicate if you have a hardware problem. It has been a while since I worked on a Sparc 5. I think the DB9 connector is the serial port that is labled "A", the DB25 Connector is labled "B". You want to use the port that is labled "A".
Set up the HyperTerminal:
COM1
Baud Rate 9600
Data Bits 8
Parity None
Stop Bits 1
Flow Control None
Turn on the Sparc 5 and hit <Stop> D. This will enable set debug-switch? = True. Turn off the Sparc 5 and turn it back on again... You should see the results of POST being displayed on the hyperterminal or tip session window.