Sorry I'm late to the thread, but...
It looks like you bought your sander, the ES 125 rather than the ETS 125, back in 2007. Has it been performing differently until recently? If you think there's an issue with it, which I think is the case based on your poll, then please contact us to help you troubleshoot it. There's no cost for the call. The service number is below in my signature.
Your sander will be out of warranty should it need repair and I'm seeing the correct tool registration for you.
It shouldn't take much pressure to keep the pad from spinning. But like others have said, let the sander and abrasive do the work. It looks like you also have the RO 125, which you can use for more aggressive sanding and pressure if needed for quick material removal.
If there's anything I can do personally to assist you, please feel free to contact me directly. I'm glad to help out.
Thanks,
Shane Holland
sho@festoolusa.com