The troubleshooting suggestions below assume the data on the drive is damaged. However, before assuming the worst, check the following:
If the Lisa configuration has been changed recently, or it has been out of use for an extended period, also check the power supply voltages at the drive.
If the problem persists, troubleshooting typically uses the following progression:
In response to some problems re-installing some early variants of MacWorks, Sun Remarketing had this advice (it may not be applicable to other OS installers):
Source: http://www.cs.dartmouth.edu/~woz/lisatech/page32_33.html ( Lisa/Macintosh XL Do-it-yourself Guide published by Sun Remarketing, Inc. )
Startup error code 84 pertains to Profile and Widget drives. It means the boot blocks are damaged. There are three possible fixes.
Fix one involves double-reformatting the drive-
Editor's Notes: Not sure that this will help anything since it doesn't make sense that one format will make a difference from another. It might help if you are using an old version of MacWorks, which sometimes gets confused if you are installing it over a drive that has existing data. If you have an Apple II or /// available, initializing the drive under ProDOS or SOS may have the same effect as using LOS.Fix two involves reformatting the drive with MacWorks Plus version 1.0. 18 or later. Holding down the Apple and the left Option keys while double clicking the MW Install icon opens the program in the expert mode. Expert mode recognizes most unmountable drives and gives the option to you to reinitialize them. Afterwards, the drive may or not be bootable.
Fix three is low-level formatting.[LisaFAQ] > [Hardware] > [Hard Drives] > [Hard Drive Problems] (Comment on this answer)