I have never had/known a keyboard without a sleep button of some description. If it doesn't actually say sleep on it, it will be the form of a new moon shape.

It is a long time since I used XP but the Power Options/Modes are different to Windows 7 but as I remember it -

If your keyboard has a sleep button on it, you can press it to put the computer in sleep mode. However, this method is not as good because the computer can be turned on again only by moving the mouse. A better method is to open the Windows task manager (ctrl-alt-delete) and select shut down and then hibernate. In order to turn the computer back on again you have to press the power button. A shortcut of this method is to select the start tab at the bottom of the screen and then select shut down. While holding down the shift key, the standby mode changes to hibernate. Once you select this, the computer will go into the hibernate mode.

There is a LINK here (you don't need to read it all) with explanation screenshot enter link description here

You can also create your own desktop icon sleep button enter link description here

Hope this all helps

Don't know if you can check this but it's a Viewsonic VX912 LCD Display.

If there is no sleep button on your keyboard then the best you can do is set up via the Power Options. Not sure why you have given me the details of your Viewsonic - it's the keyboard model you should have given me - however you seem certain that there is no sleep button which I find rather odd.

To get back to your original query which was to do with the "dodgy" button on your Monitor. The only solution would be to ask a local computer firm if it is possible to do a repair for you asking for a full quote first.You say it has served you well for a few years but failing a repair it may be time to invest in a new one. Plenty of choice these days and plenty of prices to choose from.