I have an IBM PC 350 P-100. When starting cold, it hangs at the boot splash screen. It won't respond to the keyboard, so I have to do a power cycle. Then it boots, but the first program I run causes the memory manager program to say that an illegal instruction was issued, and the machine goes into an infinite loop. Then I do a soft reboot, and it boots up and runs fine. The system has no USB ports. It boots OK from a floppy, just not from the hard drive. I am running FreeDOS on it. Disk check programs and a memory test program report no problems.
That is very common for older ISA devices. They are very specific in their resource requirements. Sounds like you had an IRQ conflict and was causing the system to crash. If I recall, IRQ 5 was a favorite of most sound cards.