Let M = "The cheese melts"
Let R = "The nachos are ruined"

[(~M ⊃ R) • R] ⊃ ~M

| M | R | ~M | (~M ⊃ R) | (~M ⊃ R) • R || [(~M ⊃ R) • R] ⊃ ~M |
| T | T |  F |     T    |           T   ||                F     |    
| T | F |  F |     T    |           F   ||                T     |
| F | T |  T |     T    |           T   ||                T     |
| F | F |  T |     F    |           T   ||                T     |

The last line is not TTTT, so it's not valid.

This is neither Modus Ponens nor Modus Tollens.

It is the logical fallacy of "affirming the consequent".

That's because it could be that indeed the cheese melted,
and the nachos were ruined anyway. 

For instance, it could be that the tortilla chips are old, 
and that's why the nachos are ruined, not necessarily 
because the cheese didn't melt.

Edwin