What System floppy are you using? It might be too new or not addressing the ROM properly.
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Also you could have a dirty ADB port. Knowing how old it is it could have some corrosion on the female or male side of the keyboard that is not letting it connect. Try the keyboard another mac if you have one that old and rule out the variables.
From wiki.
[Although it uses 32-bit instructions, the SE/30 ROM, like the IIx ROM, includes some code using 24-bit addressing, rendering the ROM "32-bit dirty". This limited the actual amount of RAM that can be accessed to 8 MB under System 6.0.8.^^[1]^^ A system extension called MODE32 enables access to installed extra memory under System 6.0.8. Under System 7.0 up to System 7.5.5 the SE/30 can use up to 128 MB of RAM. Alternatively, replacing the ROM SIMM with one from a Mac IIsi or Mac IIfx makes the SE/30 "32-bit clean" and thereby enables use of up to 128 MB RAM and System 7.5 through OS 8.1.
A standard SE/30 can run up to System 7.5.5,^^[4]^^ since Mac OS 7.6 requires a 32-bit clean ROM.^^[5]^^
Additionally, the SE/30 can run A/UX, Apple's older version of a Unix that was able to run Macintosh programs.^^[6]^^
Though there was no official upgrade path for the SE/30, several third-party processor upgrades were available. A 68040 upgrade made it possible to run Mac OS 8.1, which extended the SE/30's productive life for many more years. The Micron Technology Xceed Gray-Scale 30 video card fit into the SE/30's PDS slot, enabling in to display greyscale video on its internal display, the only non-color compact Mac able to do so.]
What System floppy are you using? It might be too new or not addressing the ROM properly.
From wiki.
[Although it uses 32-bit instructions, the SE/30 ROM, like the IIx ROM, includes some code using 24-bit addressing, rendering the ROM "32-bit dirty". This limited the actual amount of RAM that can be accessed to 8 MB under System 6.0.8.^^[1]^^ A system extension called MODE32 enables access to installed extra memory under System 6.0.8. Under System 7.0 up to System 7.5.5 the SE/30 can use up to 128 MB of RAM. Alternatively, replacing the ROM SIMM with one from a Mac IIsi or Mac IIfx makes the SE/30 "32-bit clean" and thereby enables use of up to 128 MB RAM and System 7.5 through OS 8.1.
A standard SE/30 can run up to System 7.5.5,^^[4]^^ since Mac OS 7.6 requires a 32-bit clean ROM.^^[5]^^
Additionally, the SE/30 can run A/UX, Apple's older version of a Unix that was able to run Macintosh programs.^^[6]^^
Though there was no official upgrade path for the SE/30, several third-party processor upgrades were available. A 68040 upgrade made it possible to run Mac OS 8.1, which extended the SE/30's productive life for many more years. The Micron Technology Xceed Gray-Scale 30 video card fit into the SE/30's PDS slot, enabling in to display greyscale video on its internal display, the only non-color compact Mac able to do so.]