Question : Managed PC Boot Agent has taken over my WIndows XP Pro computer

I needed to install a new wired/wireless router on my home "network." The network normally consists of a Dell Dimension 4100 running under Windows XP Pro SP3, a Dell Inspiron 1520 running under Windows Vista Home Premium SP2, a Dell Studio 1555 running under Windows 7 Home Premium, a printer hardwired to the XP machine and shared with the two laptops, and a router (wired for the XP machine, wireless for the two laptops).
I bought a new Cisco E2000 router and proceeded to set it up it from the XP machine, using the CD-ROM provided by Cisco. As best I can tell, the router setup is now working fine. But at the end of the setup process the XP computer froze when I attempted to quit the setup program.
The router setup program apparently left behind a Pre-boot management program which was supposed to run a clean-up program from the CD-ROM after the next restart. However something went wrong. For a while a could not get a normal Windows boot, but I would get a Safe Mode boot. Now I can't get past the pre-boot management program. It keeps telling me I have an invalid boot diskette (with instruction to "Insert BOOT diskette in A:")--even after I removed the floppy drive from the boot sequence (I can get to the BIOS setup). If I do insert a bootable diskette in the A: drive, the computer won't look for it.
I was hoping to be able to do a Windows Repair from the original Windows installation CD-ROM(s), although I don't know how well that would work since my initial Windows install was XP Home, then I got an upgrade CD-ROM for XP Pro (so I don't have a normal installation CD-ROM for XP Pro). However I am unable to force the computer to boot from the CD-ROM drive.
With this problem and my current skills set, I can't manipulate anything on my boot drive
How can I get this Pre-boot manager out of the way?

Answer : Managed PC Boot Agent has taken over my WIndows XP Pro computer

 I have to agree that I can't see a logical reason why an installation program should cause the near-catastrophic problem I described. I'm still suspicious there is a connection, but I can't prove it. I am NOT about to repeat the process to test any such hypothesis, so that question will remain forever unanswered.
  Early on I had pretty much ruled out BIOS setting changes and cable failures. But my problem HAS now been resolved. My initial call (online chat) to any technical support was to Cisco/LinkSys. That got me nowhere, except to realize that the particular rep I was trying to communicate with was paying no attention to what I was saying. The next attempt was with Dell--this one could be described as "close, but not cigar." The first suggestion from that rep was that I needed to clear NVRAM; it turns out he was right, but unfortunately he did not know the necessary steps to take on this particular Dell model. Yesterday I finally happened to run across a discussion on Wilders Security Forum about someone else's similar problem. I performed the NVRAM-clearing steps described in that discussion; lo-and-behold, upon the next power up I regained access to all my internal mass storage devices. Those steps are: remove ALL power (AC and battery) and hold the power button in for 20 seconds. I am now hastening my migration away from this computer, hoping to complete such migration before happens again.