Firstly make sure you are using only the Numberpad with the Num-Lock key turned on.
Remember also that some programs don't support ALT key functionality, so it might not be a specific problem with your hardware, but might be an issue with the program you're using if that program has changed. If it doesn't work with [Alt] does it work with [Alt Gr]?
If your keyboard has a [Function] key, try holding down the [Function] key with the [Alt] key and typing the number sequence. For example [Function] [Alt]  and see if that works.
As a workaround method, although I'm not suggesting you use this as a permanent solution, you could open the Character Map:
Start > All Programs > Accessories > System Tools > Character Map
and copy and paste the characters manually
Yet a further alternative workaround, which you could use as a permanent solution, is by using Autohotkey and setting up a hotkey to automatically insert a specific character when you push your hotkey, for example you could bind [Alt]  to insert [é] - once you set that up, it will function just as well as your [Alt-130] method you were previously using.