2007 macbook - trackpad stuck in scrolling mode
Sometimes issues like these can happen if there is water underneath the trackpad. Try blowing some air or warming it out in the sun or other dry area. 

Try to use an external mouse and you should know if the USB bus is still working.

You can refer to iFixit to open your MBP and remove the small dust particles which maybe cause the issue or try to reinstall OS X and see if that fixes the issue.

There are mouse controls via keyboard if you need to get around or avoid a repair. 


https://support.apple.com/en-us/HT204434