Why does my laptop button press itself?

A bad keyboard generally causes this. Depending on the model and whether even the modern Packard Bells build the keyboard into the palmrest like the big three here in Murica (Dell/HP/Lenovo), you can disconnect it to confirm for sure. If the keyboard is fused, you may have to do partial disassembly; usually, opening the bottom and disconnecting it is enough—the motherboard rarely needs to come out.

There are two strikes against me when finding parts: I do not know the model, and we have not had Packard Bell here since 1999, so there's limited information on parts and no parts supply for them. They were owned by Acer Group for a long time, so depending on which crop of model you have, it's probably removable with a pry tool by unlocking the keyboard. There's a good chance it's an Acer or Gateway P/N for the UK/EU keyboard (or the region you are in, most of the time when you see a modern Packard Bell it's un the UK or EEA) and you can use that in your favor. That's how I would approach it if someone brought me a Packard Bell to fix, being in the US.