Hi my logitech wireless keyboard/ mouse died last week. I took it to their customer service center (in the boonies of Tsuen Wan) and they repaired it on the spot for free- it has a 3 yr warranty. Kind of a pain going all the way out there, but the keyboard/ mouse did cost about HK$400, so the travel costs were cheaper than buying a new one. Have you checked into the warranty on your kit?
change batteries
re-connect the bluetooth (ie. delete the keyboard+mouse from bluetooth in control panel and start over)
make sure you have a regular keyboard/mouse handy!!!
Sit your keyboard close to the infrared box thing(or whatever you call it). Kinda defeats the purpose of a wireless keyboard but at least it will/may work!