There are a few things I've seen that can be causing this ranging from anywhere between a faulty hard drive partition, or a failing video graphics card. What I recommend trying is to use the recovery mode and if you can utilize the systems disk to repair your computer if it is just a hard drive issue. If not you may have a deeper concern here. Let me know how it works out for you and if no progress has been made I will continue to help troubleshoot.
For the heating issue, I'd pull the fans, use canned air to blow them out and clean the vent behind them. Here's how: MacBook Pro 15" Core 2 Duo Models A1226 and A1260 Left Fan Replacement
Video issues may be coming from the nVidia 8600 GPU which had issues and a previous recall that has now expired.