You have to replace a V-Belt, and you can't get to it.
Don't Panic, read on.
Step 1: How to Sneak in a V-Belt
V-Belts are commonly used to drive the accessories on the engine of a car. The common configuration shown has the crankshaft pulley driving the water pump (vital for cooling) and alternator (charges the battery) with V-belt A and the power steering pump and AC compressor driven by the crankshaft pulley and V-Belt B. The crankshaft turns, and everything turns, you have heat, AC, power steering, and you don't run down the battery. Most important, you don't overheat the engine. As things wear out, you may have occasion to replace one or the other. It's best to replace a belt when worn instead of broken, that way you're not in a pickle.
I've seen this configuration on cars by Geo, Volvo, Mercedes that have the engine in a fore-aft direction. It shows the belts and pulleys as you might see them looking through the radiator towards the engine and everything behind it.
Step 2: You can't get there from here
So you have a bad belt and look, you can't get to it because the pulley that you would adjust to slacken belt B (the light one) won't play nice. If you lack the leverage, heat, lubricant and time to move it. A (the dark belt) is too small to loop around all of the pulleys ahead of it, and the motor, mounts and such are behind belt A. It looks like you can't get there from here. But you can, read on.
You can slacken the alternator tensioner to get belt A off of the alternator and the water pump, or just cut it if it isn't gone already.