If you're dodgy you can try using a slightly finer grit (2-300) sandpaper on the belts ribs to remove the glaze from the pulleys.
Worse case scenario, you still need new belts and wasted an hour scuffing them up.
To confirm its the belts, if you have access to some, you can try dry lube.
If they shut up for a minute or two, it's most probably as above.