I have to type in French as well as English but do not wish to change language. I need to type in accents and have always used the number key pad - eg. control+ ALT + 133 but recently my keyboard wont allow this. How have I lost this facility? Using the insert button + symbol is more time-consuming. What can I do?

Any new hardware or software?

Since this is a new problem try a System Restore to a point prior to the problem:

start > All Programs > Accessories > System Tools > System Restore