I have a Dell flatscreen monitor model #E173FPb that turns itself on and off during use. How do I fix the switch, or is it something worse?

It can be failing power supply due to bad caps, or bad solder joints, or failing inverter circuits.
If you are going to DIY and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply (they should be replaced in a set), blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed DELL monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.

Basic LCD monitor troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting

http://en.wikipedia.org/wiki/Capacitor_plague
Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.
Replacement board: http://www.lcdrepair.us