optiplex 755 w/not boot no video

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I have acquired an Optiplex 755 MT XP Pro in a not working condition. It seems i might have two problems at once. First, when i press the power button, i hear the fan running, no beeps, no diagnostic lights. Since the system will not boot, i use the power button to shutdown and when i release the button the system attempts to restart, while the power button remains solid yellow only and always. Consequently, i have to remove the power cable to keep the system from consistently attempting a restart. I am using my working monitor, tried reseating memory sticks, checked all cables on mobo. The t/s guide does not seem to address this situation the way it exists. The mobo is p/n 0gm819 with on board video. There are no cards except for a modem. 

Any idea?

Please help.

Thanks!

I didn't find the right solution from the Internet.

References en.community.dell.com/support-forums/desktop/f/3514/t/19412334

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