Minolta SRT-101 stuck

Hi all, Does anyone please know how to get one of these 'unstuck'?
The advance lever can't be moved past the first couple of centimeters (but can be brought back to the resting position). The film sprocket rotates freely in both directions, probably because the sprocket release button on the bottom is pressed in and stays there (is this how the camera became stuck maybe?). There are not enough buttons on this model of camera to try pushing, so I tried to unlock it by actuating the self timer lever, which now doesn't run past midway...
The camera worked fine until yesterday but now I'm running out of ideas. Thanks in advance for any tip.
kr,
Benny