Overheating cause of frozen screen

MY COMPUTER has recently developed an exasperating problem: it unexpectedly freezes up. I might be typing a letter or monitoring the stock market when it suddenly hangs. My only recourse is to power down and restart. I have lost valuable data many times because of this problem. I am about ready to throw the thing through the window. I recently added a high-speed internal modem and sound card. I thought they might be defective and had them replaced. The freezing problem persists. What can I do? CLIFFORD WOO Mid-Levels It is good that you mentioned the addition of the new cards. Ironically, your ''freezing'' problem might be due to heat.

As you add new function cards to the computer, they generate more heat while blocking the normal air flow through the computer's case. It is possible that extra heat is causing the computer to malfunction.

See if your system has a built-in fan. If so, make sure it's not pushed against a wall or blocked in some other manner. Restricted ventilation can cause the computer to overheat. Typically, an overheated computer will lock up or act erratically.

If your computer is not equipped with an internal fan, make sure enough air flows through the computer case. The best way to do this is to add an internal fan. Several companies make them; the problem is finding room for the fan and wiring it into the computer's power supply.

Another way would be to try a device made in the United States about which I read recently.

Called the FanCard, this gadget is made by a company called T. S. MicroTech. It looks like an ordinary interface card and plugs into a standard eight-16-or 32-bit computer slot.

Depending on the model, the FanCard-I (US$23.95) or the FanCard-II (US$44.95) has either one or two miniature fans built directly into the card.