Answer:
User C.
Step-by-step explanation:
As per the given details, the problem of user C's system must be addressed first due to the seriousness of his case. His computer is excessively overheating up to the smoking point and if his problem is not addressed soon, it will damage the vital parts of the computer or may also explode. The other users having the problem of inability to access the internet or issue of forgotten password can be addressed later as these are minor problems that do not have as such consequences. Thus, user C is the correct answer.