Space bar, left-side enter key and backspace do not respond.

You move the carrier, with the space bar or backspace key, to where you want the margin to be set.
If the carrier stops before you get to where you want to set the margin, then locate the ALT key at the bottom left on the keyboard, hold it down, then locate the key directly under the words above the keyboard that say M REL (the 3 key) and push it. Then move the carrier with the space bar or backspace key. (whichever direction you want to go)
When the carrier is where you want the margin set, hold down the ALT key and push the key under where it says L MAR (4) to set the left margin, or R MAR (5) to set the right margin.
The ALT key works with all the functions listed above the keyboard.
The CODE key works with the functions/charachters printed on the keys themselves.

if the keyboard is too old and if you have used it a lot, then ou have to replace the keyboard. The space bar alone had gone.

Its not the problem with the keyboard or the mouse
it seems that you need the full system scan..
of if you have wired keyboard and mouse connect them to the computer and check using them with the same browsers ... which will determine where the problem is ?

if the wireless keyboard and mouse are working fine
then need to update the drivers
or there is some problem Hack / Virus scan (not sure) but don't worry it could be a magnetic effect of speakers or monitor
you have to check them out

1. Go to the manufactor's website.
2. On the website there should be a search bar either in the top or bottome of the page.
3. Enter your keyboard model number into.
4. Under the support or drivers tab, make sure you have the correct drivers and current firmware. for your keyboard.

test with other keyboard.. if space key working then new keyboard is faulty and go claim warranty.. can also try the new keyboard on other PC or notebook just to make sure..

If the mouse works fine, then there's no problem with the wireless donggle. If there are some keys that are not working, you need to contact the manufacturer for RMA.

You have stuck keys from when you removed to clean. Remove the stuck keys and see if it works OK when you press the rubber cap instead of key
The back space one may have a link under it if it is a wide one ensure it is fitted correctly

right click in keyboard. you can find in the space bar line "

from left;
CTRl, logo windows, Alt,space bar,Alt,Logo windows,right clickkey,Ctrl.

You can identify right click key cause there's an arrow pointer on it.

I had this problem for a very long time as well. Turns out this is an encryption issue. It's off-balance. You need to reset the encryption, and here's how:

On the LEFT side of your wireless keyboard press and hold Ctrl+Alt, and press F12, then release all three buttons. Now push the Connect button on your Wireless Receiver, then the connect button on your wireless keyboard. Now press Esc. Try it. See if it works. It did for me.

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.