Turn on computer: BLACK SCREEN message

I just re-installed Windows XP on my Dimensin 4550.  I had to do this due to registry error and not being able to fix it at all.

Now, whenever I reboot the machine or turn it on at first, there is a black screen with the option to "select which operating system...etc"

It gives me two choices which are both the same"

Windows XP Home Edition

Otherwise, it states that the system will open normally in 25 seconds etc...

How do I bypass this screen each time?  It never did that before.  I thought that I installed XP after I took everything off the hard drive.  Is this happening because it thinks that there are two OS in this computer?

~Jackie