Blockland needs about 512 MB of RAM to run efficiently, and an 800 MHz (WAY less power than processors of modern computers) processor.
You CAN run Blockland fine, I think that either the following is wrong:
1) Your computer STILL isn't getting enough airflow. Just by another fan for it, a REAL computer fan, or get liquid cooling.
2) Your RAM is corrupt. Take out your current RAM, go to a computer store and ask for a 1GB RAM stick for the same type of RAM you have. Remember, there ARE different types of ways that the connector parts of RAM are made in, so be absolutely sure you have the right one.