Questions regarding power supply & computer specs

I am currently working on an emachine with a bad power supply. After doing some checking, seems to be a common problem, usually right after the warranty expires. This system has a 150W power supply. When back probing the connections under a load, I get no power readings at all. Gateway will not tell me if it is the power supply or not. The person who brought this system to me for repair said it has slowly degraded, shutting down after booting, refusing to turn of at the on / off switch (need to use power cord to start / stop). The processor fan comes on, the power supply fan comes on, the power light on the front of the PC comes on. Nothing boots, no POST, cannot reach CMOS. Cannot boot from floppy. One CD/DVD drive opens & closes but the second one doesn't. Anyone have any suggestions on what I am dealing with here? I really dislike troubleshooting Gateway's. Their support is so vague in what they tell you. They keep telling you to run the same test over and over. They don't appear to read my list of diagnostics that I have completed.
The power supply is a ATX-250-12E 60/50 mHz Rev P7. The system is a T2865. I want to put a larger power supply in, but don't know what other things I need to change to line up with the new supply. Any and all suggestions will be appreciated!
I have a hard time believing that a 2800+AMD Athon Processor, 160 GB hard drive, Nvidia GeForce MX graphics and 8-in-1 media reader, CD drive, DVD RW drive can run on this power supply!

 

Who is a reputable company that will send a response to my compatibility query? I decided to take your advice and go with a 400W. Just am not sure where to find the ps I need!
Thanks!

 

I, too, live in a small town. Our one and only computer repair shop up and left. My ISP is satellite. No help from them at all! They can't even get my dish pointed!
Thanks for your help! I will keep looking for something to match up!
D