Yamaha DTXpress/DTXplorer/DTXtreme

I have a older desktop (tower) PC that connects to my DTxpress I to 
serially control my drum brain set at PC-2 connection.  Everything 
works good with this setup.  The problem is I want to connect my 
laptop in the same configuration, but my drum brain always gives me 
an error: ERROR HOST IS OFFLINE.  I'm fairly knowlegeable about PCs, 
so after playing with BIOS, DRIVERS, SETTINGS, it still won't see my 
laptop.  So after giving up I hooked my desktop back up, turned on my 
desktop, turned on the DTXpress right after, and it worked without 
error before the PC even got through the BIOS boot.  Does this tell 
me that it is a voltage or line level that the brain is triggering 
off of?  The serial port in my laptop does work, (I have pinged), and 
the ports should be universal (pinouts) with one another, correct?  
Thanks.  Shuman