Another Hardware Issue

[Doug Hardie]

I have another machine which will not boot the first time after a  
power on.  It gives the following messages:

Mounting root from ufs:/dev/ad0s1a
panic: vm_fault: fault on nofault entry, addr: c6303000

syncing disks... 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
giving up on 1 buffers
Uptime: 16s

However, if after that you hit any key on the console or the reset  
button on the front panel it will boot and run just fine.  This is  
running FreeBSD 4.6.2-RELEASE-p13.  It has run fine for years until  
this started.  There is no point to updating it as it has no users.   
It has no running services.  It only sends a couple of status emails  
daily and does frequent rcp's to my production servers.  Are we about  
to lose the motherboard?