I have a PS/2 Keyboard and Mouse.
When I try to start MenuetOS from floppy (from menuetos.org), it hangs at the blackscreen where it says "Press ESC to start". However, if I disconnect my mouse, it starts fine, but then I only have keyboard. I can take another mouse, serial COM1, and all works fine. But both PS/2 keyboard and PS/2 mouse hang.

My system:
CPU: Pentium IV Northwood 1.8GHz
Mainboard: ASUS P4XP-X
RAM: 512MB
Video: Radeon 9000 1280x1024

I can provide more information if anyone tells me how to get more information.

It looks like some problems with enabling A20 line while a PS/2 device is attached. Try changing BIOS settings about emulation/legacy stuff maybe the BIOS is trying to emulate a PS/2 mouse/keyboard via USB with SMB code.

It happened to my SolarOS also with some laptops... some return an extra byte or an extra IRQ or other data...

The more advanced stuff would be to try and debug the A20line enabling code...

i checked my BIOS and i did not find any such option

Usually OS hangs with PS/2 when motherboard is starting to deteriorate (was that the right word) so check your capacitors - if they are like inflated then put your MoBo in the fridge or buy a set of new capacitors ($10x6 or x8 ).
I cracked my brain reinstalling XP and blaiming on programs and patches until I figured this out. Sometimes works - other times its just fine . Maybe its the fault of MenuetOS or ASUS board's incompatibility, but usually its hardware.

BTW, you have 512 posts
Dare you answer me and you must answer yet another 512 timest to get 1024