For a nikon coolpix 520--after a firmware update, I've got nothing on the setup screen (wrench) but the firmware version. How do I restore the setup screen items?

Reset All Press the d button M z tab M Reset all
When Reset is selected, the camera's settings will be restored to their default

I would suggest you go to the Nikon support site and see if there is a version you can download from there.

Press your camera's Menu button and scroll to the Setup Menu (wrench symbol). Scroll to item 10 in the Setup Menu, "Reset All".

Confirming the firmware version:

1. Turn on the D80
2. Press the MENU button and select Firmware Version from the setup menu. The camera's firmware version will be displayed.
3. Turn off the D80

Basic Upgrade instructions: for detailed instructions, see pdf files below.

1. Download and expand the firmware files
2. Format an approved SD (Secure Digital) memory card in the camera
3. Connect Camera to computer (in MSC USB mode) or use a SD Card Reader
4. Copy to the top level of the card the downloaded "A firmware" file
5. Disconnect camera from computer
6. Update the firmware from the "Setup" menu
7. Follow the camera's on-screen menus
8. Repeat steps 2 through 7 using the "B Firmware"
9. Re-format Card

D80 1 11 firmware upgrade Nikon Knowledgebase

Check your current firmware version before beginning:

1. Turn on the camera.
2. Tap the menu tab at the bottom of the monitor to display the setting controls and tap Setup (wrench icon)
3. Tap Firmware Version in the Setup menu(wrench icon)
4. The cameras firmware verison will be displayed.
5. Turn off the camera.

Basic Download and Installation instructions: (New firmware versions contain all previous versions.)
Windows

1. Create a new folder with an appropriate name on your computer's hard disk.
2. Download F-S4300-V12W.exe to the folder created in step 1.
3. Run F-S4300-V12W.exe to create the folder titled S4300Update, containing the following:
   
   
   • firmware: folder containing the firmware.bin file
   • firmware.bin : the firmware located inside the firmware folder.
4. Insert the memory card containing the firmware folder into the camera and turn on the camera.
5. Tap Firmware version in the Setup menu and follow the instructions displayed to upgrade the camera's firmware.
6. After the upgrade is complete, turn the camera off and remove the memory card.
7. Check the Firmware version item in the setup menu to confirm that the camera's firmware has been upgraded.

For detailed instructions, please see the PDF files below.

Macintosh

1. Download F-S4300-V12M.dmg.
2. Double-click the F-S4300-V12M.dmg icon to mount the disk image titled, F-S4300-V12M.
3. A folder titled S4300Update, containing the following files, will be created inside the disk image:
   
   
   • firmware: folder containing the the firmware
   • firmware .bin: the firmware
4. Insert the memory card containing the firmware folder into the camera and turn on the camera.
5. Tap Firmware version in the Setup menu and follow the instructions displayed to upgrade the camera's firmware.
6. After the upgrade is complete, turn the camera off and remove the memory card.
7. Check the Firmware version item in the setup menu to confirm that the camera's firmware has been upgraded.

COOLPIX S4300 1 2 firmware update Nikon Knowledgebase

I'm convinced you already did read the user manual. There are three things you can reset:
1. User settings. In menu mode P, you can undo all the settings you made. Page 69.
2. Reset all settings. Page 151 Menu settings, chose the wrench symbol and chose reset all. All settings will be restored to factory settings.
3. Reset file numbering. Page 154 Menu settings, chose the wrench symbol and chose reset file numbering.
In the same menu is also the view firmware version. Yours should read Coolpix P90 Ver.X.X .
The latest update of firmware for the P90 is 1.1 Great chance your camera came with that revision already. If you registered your camera with Nikon, they will inform you when a new firmware is released.
Really, there is nothing more you can reset on the camera.
So if something is wrong, it can't be helped with the reset you have in mind, because that reset does not exist.
If you want the firmware 1.1, goto Nikon USA and support. Everything you want is there.

the default time is set to military. in the setup menu find the default settings and change the time setting.

Only 3 options show but you can page down for more options

That's the bug in Nokin L100, update the firmware version from 1.0 to 1.1, this will solve the battery exhaust problem. Firmware version 1.0 has only 2 battery (Alkaline and Lethium) option where as Firmware version 1.1 has Nickle battery also. But, to update the firmware you need to have EH-67 AC Adapter to give power to the camera.

If you are using alkalines, this will always happen. You need to use rechargeables, or special high current disposables, eg "Oxyride".

A good solution for this camera is to use a single CRV-3 disposable lithium batteries. The battery life is long and they are light weight too.