Key board few keys on my keyboard are not workin suddenly like back space, esc, H, G and also windows key. please Help me out.

What type of symbol is it? Exactly which row and what key is it?

change your keypad of your lap

The laptop keyboard will need to be replaced, go to www.ebay.com type make and model of laptop, refine search to keyboard.

if you have windows Xp installed see on microsoft site:http://windows.microsoft.com/en-US/windows-xp/help/on-screen-keyboard
using kayboard: Display the Start menu by pressing Ctrl+Esc (or the Windows logo key). Move to All Programs by pressing P. Move to Accessories by pressing the Down Arrow key and then Enter. Press Enter again to move to Accessibility. Move to On-Screen Keyboard by pressing the Down Arrow key and then Enter.Or using mouse: Display the Start menu by pressing Ctrl+Esc (or the Windows logo key). Move to All Programs by pressing P. Move to Accessories by pressing the Down Arrow key and then Enter. Press Enter again to move to Accessibility. Move to On-Screen Keyboard by pressing the Down Arrow key and then Enter.

There is't really such a thing as four main keys. Ctrl, Alt, Shift and esc/del are used a lot for shortcuts.
Comment back to clarrify what your talking about if this doesn't not answer your question.

What kind of device is it? A normal keyboard has the ESC key in top left corner.
If you are using a Windows device run the "On-screen Keyboard" and click the ESC key with your mouse - better than nothing. (Find the on-screen keyboard in the Start Menu under Accessories - Ease of Use)

Try using the "CTRL" key as a modifier (Holding it down) and then press the "ESC" key one time. This should get you by for now. As for the not working Windows key. You could have a number of mechanical failures there. All depends on how the board is put together. You will likely need a new board, but if you find that the "CTRL" + "ESC" key combo doesn't work either, then this could even turn out to be a software issue. You might want to verify that all other keys work on the keyboard. You might find a dead region.
Good luck!

One of your ctrl key is stuck. try to pull it up. Take a vaccum cleaner put it on medium blower keep your keyboard upside down and blow keboard from sides so that whatever is blown falls down on ground.

if you don't have a window key on your thinkpad t43p keyboard, you can use an alternate keys:
i.e., Ctrl + Esc (press Ctrl and Esc key's) Please rate my answer.