1) prompt returns a string, the comparison is with numbers - incorrect
2) blocks with if ()... you are always comparing with constants, although earlier they announced their "meaning"
Accordingly, it would be better to do so:
1) var trouble = parseInt(prompt('What is wrong?'))
2) if (trouble == cabel) {...
...
else if (trouble == router) { ...
...
else if (trouble == computer) { ....