installed antivirus 2009 did updates and now xp won't boot

Hello all,

 

I installed Norton AV 2009 on an xp home system did the updates and now I receive the system bios message no disk available.

After booting from my xp cd and using the Repai, then using fixboot, I was able to boot the system up again.

 

So what is wrong with Norton that is now giving me this headache?