you have to get a new button, that isnt the easiest job to resolder one on, took me a while and a lot of patience to do, any SP tech or SP themselves should be able to do it, other than that, a new board or a replace one is required
Soldering a new button on there is a bit tricky unless you have experience soldering SMT, instead you might want to solder wires on there going to a membrane pad. At least then the same problem isnt going to happen again.
If you need any advice on soldering, or someone to do it for ya for the price of a beer, PM me
The lucky stage 4 board with SP noid is probably the cheapest, retailing at £67.
The lucky stage 4 board with Mac noid is the most reliable and in my opinion the best ion board out, it retails at £81.
These boards are sold out at Lucky Europe, and heavily backordered in the US. So you will need to find a dealer that still has some in stock or find one second hand.
Whatever board you go for make sure its compatible with a membrane pad. The Ion button is a pain in the ass.