Inspiron M5030 - Power button not working and 5 beeps

Hi. I have just purchased a 2nd hand Inspiron M5030. I got it, turned it on and it booted up fine.

I bought it knowing the keyboard didnt work so i took the laptop apart, reseated the keyboard and it worked fine.

I had to take the panel off that surrounds the keyboard and holds the power button and the mousepad. This involved unplugging the cables from the mobo. I had to do this as the keyboard wouldnt fit properly without doing this.

Since then, the power button doesn't work. The only way i can power on the laptop, is to remove the CMOS battery, wait a while then plug the charger in - this powers on the laptop. I get a 5 beep code doing this - assuming its where i removed the battery.

I have another power button from a different inspiron model which has a small LED on it, this LED lights up but the button still doesnt power on the laptop.

Why would the button just stop working like that?