My iMac not turning on.

If the system was running, then the fan cranked up and then the buildings power goes out implies you encountered a power surge from the power company. Did you see them out and about your streets trying to get the power back on? Sometimes the line transformers short out driving a high voltage spike down. Do you use a power surge suppressor or a UPS? Is your telco or cable connection also protected?

It might be wiser getting a new system as the needed parts is likely to exceed the cost of just getting a used working system, as you are heading to collage a laptop maybe a better system for you like new M Series MacBook Air system which will offer better performance and is something you can carry to class.

Recovering your stuff might only need an external SATA HDD case to slide your internal drive into. The only tricky part here is the cases ports need to interface what the replacement.