DELL Dimension XPS T800r CMOS Maintenance Mode worries...

Greetings, good people of the DELL universe!

I am working on a DELL Dimension XPS T800r desktop for a neighbor.

Original complaint: No video

Some things have changed since yesterday when I worked on it, so read on...

Here is what I have done so far in order:

(855) 935-7526 ***. Swapped video cards from a known good donor.  No change.

2. Discovered the DIAGNOSTIC LIGHTS on back panel.

3. DIAGNOSTIC LIGHTS remain DARK during attempted boot-up.

4. Consulted DELL documentation to learn about DIAGNOSTIC LIGHT codes.

5. Code is: All DARK - Power up default.

6. Again consulted DELL documentation to identify what to do:

   a) Reseat Microprocessor

   b) Remove all expansion cards

7. After doing both.  No change.

8. Using previous computer knowledge, I pulled EVERYTHING from the motherboard except power connections and front panel connections.  I disconnected all disk drive power connectors as well.  I left only the CPU fan connected to the motherboard.  I checked the power supply voltages against the DELL norms and all is good.

9. Now, knowing about CMOS batteries, I checked the voltage in-board.  It was 3.1VDC.  Seems good.  I did NOT want to remove it, so in order to be sure it is connected securely, I rotated the battery in-socket to create a better connection.  This is where things changed from yesterday...

10. Leaving the board BARE, I plugged in the power supply.  Silence.  Only the amber light on the motherboard was lit.

11. I installed the CPU and VIOLA!, the DIAGNOSTIC LIGHTS flash YELLOW for a second and both fans spin up quickly and then stop altogether.  The amber light on the motherboard remains lit. 

12. DELL documentation shows this code to represent: System board is receiving power,
but the BIOS is not executing.

13. I believe rotating the CMOS battery created a better connection (the computer IS almost 16 years old) thus giving me a response to power-up now.

14.  I began the process of re-installing everything and documenting what happens after power-up.  Nothing changes past that point.  DIAGNOSTIC LIGHTS flash YELLOW briefly, and the power supply and CPU fan spin up for a second, then stop.

15.  DELL documentation suggests putting the system in MAINTENANCE MODE by means of the CMOS jumper

This computer is almost 16 years old and the owner most likely does not have the BIOS settings recorded.

This is what is installed, front panel:

A CD-ROM drive

An IOMEGA Zip drive

A floppy drive

Now to the question:

Since I have no way to back-up or retrieve the CMOS settings, I am hesitant to put the jumper into MAINTENANCE MODE to see if the computer will boot all the way up.  I don't want to potentially render the computer useless by using MAINTENANCE MODE or changing the battery, although I'd like to replace the battery due to course of action because of age.

From DELL documentation:

NOTICE: Entering Maintenance mode returns all settings in the
system setup program to their defaults. Dell strongly recommends
that you record or print all current settings before entering this
mode so you can correct them when the system is reset to Normal
mode.

What do you think will happen if I reset the BIOS to default by moving the jumper and replacing the battery?

Will I cause a catastrophic failure?

Now, the flip side to the coin is that the system is relatively basic, so me having to enter boot sequences and such isn't a big deal.  I hope...

At worst, I'll have to use a drive caddy to retrieve her data from the hard disk.

Thanks in advance for all your help and assistance!

Austin Cajiao