My programmable keys are no longer programmed.

The Logitech s510 cordless keyboard does have a reciever. It's a mini usb reciever .

http://forums.logitech.com/t5/Keyboards-and-Keyboard-Mice/Wireless-Keyboard-and-Mouse-S510-not-recognized-via-USB/td-p/25956

there is a blue button next to the richt alt key on the keyboard press and hold this then press either of the following f9 mode, f10 set, f11 alarm and f12 start stop hope this helps

I was going to type this out but found the help on logitec is pictorial and might make more sense ;-]
Q: Customizing my S 510 Keyboard Function Keys with Logitech software (SetPoint) How do I use Logitech's Mouse and Keyboard software (SetPoint) to customize my S 510 keyboard Function Keys?
Cordless Desktop S 510
Model Number:
Y-RAK73 (Keyboard)
M-RBN114 or M-RBG114 (Mouse)
The Function Keys, or F-Keys, are the keys on labelled F1 through F12 above the number keys.
NOTE: To use the programmed F-Key, make sure to toggle on Enhanced F Keys Mode by pressing the F Mode key. The F Mode LED on the receiver will be off in Enhanced F Keys Mode.
Similar to the Programmable Keys, the F-Keys can also be programmed to perform certain functions.

1. Click the My Keyboard tab on the top of the screen and select the Keyboard F Key Settings tab on the left.
   
2. Select the F key you wish to customize.
   
3. Now select the task you want the button to perform under Select Task. You can also click Help to find detailed descriptions of these options.
   
4. Click on Apply then click on OK to close SetPoint.
   

The keyboard only works in basic functionality on a linux system media keys may not be support without a third party interface.

At the top of the keyboard are the LCD function keys (F9 - F12). Press and hold the function key (FN, next to the left alt key) and press F10. Use the up and down arrows to change the time. Press FN + F10 again to change between hours, minutes, month etc.

got this off the logitech forum, The only instructions that I can find (which came with my relatively new pc) are on a large "Installation Guide," the most pertinent information from which is about setting the time and date: "To enter time/date setting format on the keyboard LCD, press the FN key and F10 key simultaneously." Also "LCD: Mode (F9): switch mode from Time/Date to Alarm to Timer to Character Count. Set (F10): press to set Time/Date, Alarm and Timer. Change batteries one by one to keep LCD settings. Remove the 4 keyboard batteries to reset Character Count to "o." Bell (f11): put Alarm On or Off. START/STOP (F12): start 01 pause Timer." The Logitech program group (should be on your Start menu) will give you further information for identifying keys, and for formatting the keyboard and mouse. Good luck.

The button opens your default email program.
Here is a good tutorial on how to fix that:
http://www.freeemailtutorials.com/microsoftWindows/settingDefaultEmailClient.cwd

i need instruction on how to program it

The only way to program a key is with software provided by the keyboard manufacturer or a third party. Without that, the keys are not programmable.

When I bought my s510 recently I couldn't use the function keys even with the software that came with the keyboard and mouse.

I had to actually download new logitech software for the s510 which allowed me to use the function/extra keys.

Navigate to:
http://www.logitech.com/index.cfm/keyboards/keyboard_mice_combos/devices/145&cl=US,EN

On the right hand side of the screen you will see 'Support Center' below it click 'Downloads,'
From there you can choose your OS w98 and language and download the software you need to get your keyboard working the way it should.