I installed a new motherboard and processor, k7s5a with AMD XP1600. Turned on power and nothing happened. All connections are tight. Removed all cards and tried again still nothing. Used jumper to clear CMOS with power dissconnected then put jumper to normal and plugged power back in. Turned on tower switch and nothing happened. With power switch still on, I removed the Cmos jumper for the heck of it and the computer booted! As if that is not strange enough, I put the old board and processor that was working fine back in and the same thing is happening to that! Any help is appreciated.

When you say 'nothing happened', if you mean that no fans ran and no lights came on in addition to getting no display, then suspect either a faulty power supply module, power cord, surge arrestor, or wall outlet.
What is your power supply's wattage rating?

ATHLON XP1600
KS75A
350 WATT PS
256SDRAM PC100.
SOUNDBLASTER LIVE CARD
VOODOO 3 2000 VIDEO
MATROX 20GB 7200RPM HD
ETHERNET CARD
When I first turned on power the fans and processor seemed to be working then after a few seconds everything shut down and could not be re-started. I have been reading some other posts and will try taking board out of the case and booting w/wo video card. Reading all the other problem posts is scaring the hell out of me LOL!. What is also very strange is the fact that my old board is doing the same thing. I have ordered a 400w ps to see if that is the problem and a stick of 256DDR 2100 MICRON RAM. I have just found this site and think it is great! Thanks for any assistance and I will update as I try different things

Have you read some of the other posts on short circuits caused by the mobo touching the case metal? That can sometimes be the problem, especially if the out-of-case test works. Just use little cardboard washers between mobo and case (where you screw in into the standoffs) to fix this.

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Windows 95: A 32-bit extension of a 16-bit overlay for an 8-bit OS that was originally designed for a 4-bit processor by a 2-bit company that can't produce 1 bit of good software!

Hello Mako

You seem to have a complex situation going and I wonder if some advanced protection system is switching off the power supply unit when a problem is detected. However, that said, I'll use my trusty diagnostic charts and see if it takes us anywhere. [I'll Email you info on the boot sequence]
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1. I'll infer that:
at start up, the PC is not dead, POST runs, there is an audible beep[the video card BIOS runs and video is enabled], and the monitor begins to display info. No error code is displayed but the monitor goes blank and the system loses power. [is that right?]
2. This is, therefore, a boot up problem.
3. BOOT
[The next question asked is] Does the system boot from the hard disk drive?
If not then then you have a hard drive problem.
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I'll break in here because from what you've said it sound like you didn't get to the stage of booting from the hard drive.
Study the boot sequence info i've sent, particularly steps 5 through 11 and see if you can find where it is going wrong.

A Point to ponder:
Video BIOS/System BIOS shadowed and/or cacheable.[in BIOS Setup]
These BIOS prog's in [slow]CMOS memory can be configured in the BIOS Setup to be copied to and run from [faster] RAM so they will run that bit faster, but if some other [nasty] device decides it's going to use that memory space and overwrites the contents, then "splat!" suddenly the BIOS prog ceases to function and , of course, the boot process terminates!

"Everything shut down and could not be restarted" you said.
This sound ominous.
Now we have a totally different situation to before.
1. The PC is dead, no fans, no lights, no life!
2. Are the power supply voltages correct?
3. [Almost certainly not, so:] Disconnect all peripherals, adaptors and the system board. Does the fan run [or are there other signs of life]?
4. if not the power supply is faulty.
5. If there are now signs of life re-connect the system board.
6. If there are no signs of life the board is faulty.
7. Re-connect one device and switch on and see if there are signs of life.
8. Repeat 7 untill a device produces "no life" or untill all devices are connected and the PC still shows life.

This completes this procedure.
If the PC Startup encounters a further [different] problem at some later stage in the boot process, Email me.

You guys are great! I will try all of your advice as soon as posible and post how it goes. I wish I had known of this site before I bought the damn board LMAO!!!!!!!!

I have learned a valuable and costly lesson! The reason that everything came on and ran slowly and then stopped was probably that I never removed a label that read "remove before installing" that was located on the bottom of the heat sink!!!! I never even noticed it and as a result I was slowly frying my processor. Boy do I feel stupid!! Now I have to wait for a new processor and hopefully everything will be ok.