CPU acting strange, no live screen upon start.

I have 2 old computers that I want to fix up

System 1
Motherboard: 775i65G
CPU: Intel P4
PSU: 500w fully working coolmax

When I install the CPU and heat sink and try to turn on the computer it won't turn on. But when I remove the processor it turns on, lights up, mouses light up but theres nothing on the screen. I'm using the integrated Intel Extreme Graphics 2 VGA plug to plug into my monitor (tried all 3) nothing shows only a no signal. I find it weird that is only works without a CPU. No beeps or anything even when memory (512MB) is removed. Should I buy a video card, CPU or a whole new motherboard.

System 2
Motherboard from HP desktop computer

This computer has similar results. But when I plug in the PSU it turns on automatically without me pressing the on button. The CPU is missing a heat sink but I will buy one after I determine that it will work. The front on button does not turn off the computer and the only way to turn it off is to unplug the machine (not sure if pwr switches are in right). The computer does not show anything on the screen. I am also using the integrated graphics on this one. No beeps or anything either.
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More about acting strange live screen start
  1. update: The heatsink (cpu fan) does not spin up on system 1 when there is no cpu (is that normal?)
  2. update 2: On system 1 sometimes when I mess around and try to turn it on, it will not turn on or it turns on then off. After a while later it turns on but still nothing on screen
  3. Work through our standard checklist and troubleshooting thread:
    I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

    If not, continue.

    I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

    Breadboard - that will help isolate any kind of case problem you might have.

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:

    You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

    Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

    If no beeps:
    At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

    The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

    You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

    This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

    If the system beeps:
    If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

    Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

    Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
  4. I see a speaker on system 2 and on the cable from the case. In system 2 there is also no way for me to plug in the 4 pin psu cable. Also the front panel buttons are different there like this (. indicates pin ,indicates empty hole) it is a pga370 board

    . . . , . . . .
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