Installation Issues

[Jake Stride]

I have had freebsd 4.9 working fine on a dell optiplex, until I decided 
to do a re-install today. However, I am now no longer able to boot 
freebsd.

The installation proceeds normally, but when I reboot the system, it 
gets to the boot manager and then reboots, and then keeps on rebooting 
everytime it gets to the boot manager.

I have tried without the boot manager and also each of the partitions. 
I have also set the / partition to bootable, but to no avail.

I am sure this must be a simple error on my part, but I have been 
looking at it for too long now, and wondered if anyone else could shed 
any light on the issue.

Many thanks

Jake