usb+floppy on old PC

[davestar]

hello all

I had try Puppy on a USB stick booted by floppy on a old PC and it was ok.
I take the floppy and USB and put them in another quit same old PC and i have a error during boot just after the selection of usb boot option:
i select case 1 : psleep=25 phome=sda1 pfile=pup-100-none-262144 like in the other PC and then i have the message

read error
Hight mem corrupted -not existing to DOS

what can i check? i have in both PC a USB mouse
it's maybe a RAM problem?