The scariest part was inserting properly all the ISA cards, some were pretty hard to put and remove. 386 CPU was soldered on the MB, we cannot replace it :-/

But it was the same in 1990 that in 2023, install spacers on motherboard, screws, PSU with AT plug, insert all ISA cards, and wire all the small wires for led/button, IDE cable, floppy cable, power cable, etc, it was a nest inside :)

Then you powered on (a big red switch on the side that made a big CLUNK) and pray everything work!

After that it was configuring your CONFIG.SYS and AUTOEXEC.BAT to load driver etc. Playing with XMS, EMM386, HMA, to gain the smallest kilobyte you can from the first 640K, else some games weren't working.