Hi, I have an emachine T3256 running windows xp. My monitor seems to turn off or go to sleep, but the tower seems to still be on. I move the mouse or press a key, but it does not respond. I thought it might be the monitor, since I hooked it up to my laptop and it did the same thing. Purchased a new monitor hooked it up and the same thing happens. The monitor and computer will sometimes work for only a few minutes and sometimes hours. Help? Let me know if you need more info?

It's most likely a motherboard driver problem. Given that Emachine drivers are notoriously hard to find, your best option is to turn sleep mode off!

A bit of advice. Emachines were built with the absolute cheapest parts possible. You should buy yourself a new power supply immediately and use it to replace the stock one. If the stock one blows, it will do serious damage to the rest of the machine.
Proper quality power supplies have things like over voltage and short circuit protection and will shut off rather than fry things. The super cheapo stock Emachine power supplies have absolutely no protection at all. Most don't even have an internal fuse.
Replace it now, thats my advice! Be pre-emtive, it absolutely WILL save you money!