Series of events leading to disk boot failure message..

[jcm15]

Hi everyone. I have read through a lot of disk boot failure threads that do not match my scenario, and would like some input on where to look next. So my mom just received an eMachines computer (my estimate is it's 5 years old - model T3256) as an office computer. It is obviously a hand-me-down from her company's main office, but came to her in working order (kind of...). I hooked everything up for her, and I turned on the system. It worked fine, but was really slow, and I could tell that it had never really had any maintenance done on it, and it was just too slow for what it was. I did a complete reformat on the system, installing Windows XP Pro. I went online and got all the necessary drivers for the hardware, and once I installed those drivers to get everything up and running, I installed all of the Windows updates. Everything was working perfectly, all hardware was operating properly, and the computer was running great. When I left her that day, all was good. She got up the next morning, checked her email, sent a couple of emails, and left for a few hours. She came back, and she had a message on her monitor saying that it (the monitor) was in power save mode (it is a Dell monitor), and to push any button to continue. Nothing would work for her. I told her to turn off the computer manually, disconnect the monitor from the computer, disconnect the power from the monitor, then reconnect everything and turn it back on. This is where she then received the Disk Boot Failure - Insert System Disk and Press Enter message. I looked at it today, looked at the BIOS, and all seemed good. I restart the computer, and got the same thing. I inserted the XP Pro disk, and pushed F2 a few times and got to the memory/hardware test screen that shows BIOS status, boot sequences, and any hardware errors. it showed a Floppy Disk Fail (80) and CMOS checksum error - defaults loaded. I looked into the checksum error issue, and started with the battery, which I replaced. I went into BIOS afterwards to update the settings, and then tried restarting the computer. It still just sits at the large "e" symbol (eMachine logo) for about a minute, then goes to a black screen with a cursor at the top left, and sits there for awhile, and finally goes back to that disk boot failure message. When I try to boot from the XP disk by pushing any button during startup, it will go to a black screen that says "Setup is checking hardware configuration..." and then that goes away and it is a blank black screen and does nothing. What is my next step here?