100 degrees is the throttling temp so your cooler is not doing it's job.
While case airflow is important, short of all the airways suddenly having gotten clogged with a pet cat or something you're issues likely don't stem from that. Check thermal compound as suggested. Check the fans on the radiator, if they're not spinning you're not going to get much in the way of cooling, and a seized up bearing in a fan is easy enough to have happen. Check your CPU settings like Computers Taste Like Metal suggested, if you're doing an overclock something could have gotten fouled up in a setting.
That said, off the cuff I'm guessing one of two things.
1. The pump on the Corsair may have bitten the dust. As AIO's are want to do after a few years and the Corsairs have had more than their share of it happening to them.
2. Your PSU might not be giving your AIO enough power. Raidmax PSU's are not exactly the most well built and it's possible the power isn't going where it's supposed to. Try testing your system with a different PSU. If you have a spare PSU or a buddy who'll loan you theirs it'll save you a trip to the hardware aisle.