Hi Penny,
the raid card is a Netraid card like 1Si/3Si, 1M or 2M since it has an alarm.
It's best to install a utility and manually start a rebuild, i guess the AUTO REBUILD feature is not enabled on this controller, if it was, it would have rebuild that disk automatically and your RAID array would have been optimal again and the alarm should have stopped.
Download the Netraid Assistant utility from here:
http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?locale=en_US〈=English&pnameOID=19399&prodSeriesId=50440&prodTypeId=15351&basePartNum=COL3578&locBasepartNum=ns-12645-1&os=Microsoft+Windows+2000+Server&tech=Software++Storage+Controller
It's also a good idea to add the Netraid monitor service :
http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?locale=en_US〈=English&pnameOID=19399&prodSeriesId=50440&prodTypeId=15351&basePartNum=COL3577&locBasepartNum=ns-12644-1&os=Microsoft+Windows+2000+Server&tech=Software++Storage+Controller
The disk with status "Ready" is the new one you inserted and that one should be used to rebuild onto.
Normally their is no reason to reboot the server for a failed disk, this is where the raid card is for after all and you don't have to come to the office on your
Sunday :-)
HTH
Kris