If it is a perfect half of the keyboard that is doing this, a chip could have failed on the keyboard. Another possibility could be that something has been spilled on the keyboard. I have seen many that where suffering from the soft drink syndrome. I was able to disassemble them, clean them and all was well. If the unit is under warranty taking it apart will void the warranty, but so will spillage. If the unit is out of warranty you might think about buying a new one, then have fun taking the old one apart and seeing what you find. If it is a spillage problem and it is sugar based only soap and water and a very long drying period can remove the substance.
I HAVE A ACER NETBOOK, RUNNING WINDOWS 7 AND HALF OF THE KEY BOARDON THE RIGHT SIDE IS ONLY USEING THE FUNCTIONS INSTEAD OF THE LETTERS. EVEN THE NUMBER KEYS ON THAT HALF ARE USEING THE FUNCTION KEYS. I DONT KNOW WHATS GOING ON. I'VE TRIED HITTING FUNCTION FIVE TIMES TO FORCE IT TO WORK BUT IT ONLY PUTS THE WHOLE KEY BOARD IN FUNCTION MODE.