I guess you installed Mint last. You can solve it reinstalling grub from ubuntu (check this for more info):
(replace X according to your drive, "sda" for example)
sudo grub-install --recheck /dev/sdX
For the power issue (fans, temperature, battery life), try adding i915.i915_enable_rc6=1 as a kernel boot parameter: in the grub menu, press "e" to edit the line of Ubuntu, and then add that to the end of the line of the kernel (starting with linux).
For example: linux /boot/vmlinuz-3.0.0-16-generic <...> quiet splash vt.handoff=7 i915.i915_enable_rc6=1
If that works, you can modify grub to have it permanent:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.i915_enable_rc6=1"
gksu gedit /etc/default/grub
And update grub, sudo update-grub
They are fixing some bugs to have that as default in 12.04. Check this.
About the wireless, do you see any network at all?