An alphabet is not functioning of the keyboard

If you mean a single key; letter 'a' for example isn't working you may need to clean your keyboard. If multiple keys are not working right this is also likely. Turn it over so the keyboard is down with the screen open and tap on the bottom of the case to get much of the debris to fall out. Then you can use a brush and/or a cloth moistened (NOT WET) with alcohol to wipe everything down, especially between the keys. Canned or compressed air can be quite useful in blowing dust, crumbs, fur or whatever away. On most keyboards you can also remove the 'caps' of the keys but it is very easy to damage them and then you would need to replace them. It is also possible that a bad key or the entire keyboard needs to be replaced. First try cleaning it, it should be cleaned ocaisionally anyway. Next: determine whether the keyboard is the cause. Plug in an external keyboard, if it has the same problem consider software causes. You can try a restart into safe mode, hit F8 while windows is loading. If it fixes the problem the keyboard is not the problem. Scan for viruses. Update your drivers. Remove any recently installed software and see if that might have been the cause. If an external keyboard works fine you may need to replace your keyboard or a damaged or defective cable. If you need to replace the keyboard you should also clean the laptop at the same time This video shows how to disassemble your computer. Clean out any dust and grime to keep it running cool, replace the keyboard (search your model replacement keyboard on line) and reassemble.