Short for Advanced Configuration and Power Interface, a power management specification developed by Intel, Microsoft, and Toshiba. ACPI enables the operating system to control the amount of power given to each device attached to the computer. With ACPI, the operating system can turn off peripheral devices, such as a CD-ROM players, when they're not in use.
Not sure what the 91C reading on your ACPI means. I can tell you that 70C is HOT for your cpu.
Clean your fans (and your entire case for that matter) with compressed air, you can pick up a little bottle of it at Radio Shack or wherever.
If that doesn't fix it, get a new heat sink.
Associates Degree in IS
Studying for Network+