Dell Optiplex 755 won't boot

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freykr

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Dec 7, 2015
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4,510
have an Optiplex 755 mini tower, while working and connected to network, the screen on my monitor started to blink and show scrambled images, then the system seemed to restart, for a brief moment I saw the system splash page "Dell Bios blah blah blah" but then screen went blank, I turned off monitor, turned it back on, I see the monitor's "View Sonic" start up image just fine, but the computer does not seem to boot, so the screen message say's "No Signal" eventually goes blank. I can hear the fan in computer running, I see lights illuminated on front bar of mini tower. I depressed and held the power button for about 20 seconds to see if it would restart, when I let go of the power button, I hear the familiar whine of the unit starting up, the CD bay light comes on for a few seconds, the lights in the bar above the power button which is where the front USB ports and headphone/microphone ports are, in that bar there are indicator lights... "LAN symbol" "2" , "3" , "4" Currently on my unit... the "LAN symbol" "3" and "4" are illuminated. If I press the power button to try to turn off, it will not turned off. I can only hold and depress power button, which the system restarts but does not boot up. I disconnected the AC power cord from back, let it sit a couple minutes then plugged it back in and I get the same result. I am currently posting this message from my co-workers similar Otiplex 755, his front indicator lights do not have "3" and "4" illuminated. Rather on his just the LAN symbol and occasional blinking of the Hard Drive activity light blinks. I'm not very computer savvy, but I am thinking maybe something in the motherboard? I am assuming the power supply is OK if the fan motor and sounds come from inside the unit? Any suggestions or help is appreciated. Thanks in advance
 
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Typically with DDRx memory they work in pairs. With Dell usually in alternating slots (with same color latches). But check your manual to be sure. Also Dell often doesn't list correct memory capacity. Crucial.com is good for capacity limits but they can miss speed ratings sometimes. If you have 8GB capacity then 2-2GB ram would work. If you can't get them in the correct slots they wont be able to "take turns" processing data. I'd suggest looking at any capacitors with an X, or K scribed in the top (designed to release pressure). If the top is pushed up, or discolored you have a bad capacitor(s). They can also leak out the bottom. A television repair shop should be able to fix them. The advantage of repair vs. replace is you don't have...
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william p

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Sep 22, 2010
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3 and 4 are error message lights. Check the owners manual (avail. on line) to see what's wrong. It sounds like something is failing P.O.S.T. You can try unplugging/swapping device,s mouse, keyboard, CD also, memory chips etc. Try making a bootable Floppy,CD, or USB on the other machine. See if it will start with the HDD unplugged. If you can get into BIOS setup go to maintenance/ Event log, SYSLOG and see what errors are recorded there. Also open the case and look for swollen or leaking capacitors on the motherboard. Check that everything is plugged in all the way inside and out.
 
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freykr

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Dec 7, 2015
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4,510


Thanks William P.

Found out that lights "3 , 4" are RAM errors. I methodically removed and tried one stick at a time of the four sticks of 1 GB RAM I have. for a total of 4 GB RAM. I tried all 4 sticks in DIM 4 at first and got different error code "123" which means "Other Error" every time, so I then tried inserting RAM sticks into each different DIM slot methodically 1 at a time. It seems that DIM 3 and DIM 4 are the problem because whenever the is RAM inserted in either of those, the machine doesn't work and the error "123" come up. So, I eventually left it with the 2 RAM sticks I now have in the working slots. Machine booted, but Windows wouldn't open, eventually did a scan and repair of windows and it opened up. Just slower response now.

I'm not familiar with how computers work or how they are built. I assume something shorted or burned out in the DIM slots in the motherboard and I further assume that if I want to make those RAM slots available again I will need to replace the motherboard,. Or.. maybe if I just wanted the 4 GB of ram again see if 2 GB sticks of that kind of RAM are available and just insert double ram capacity sticks in the 2 working slots?

 
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william p

Splendid
Sep 22, 2010
3,788
100
30,340
Typically with DDRx memory they work in pairs. With Dell usually in alternating slots (with same color latches). But check your manual to be sure. Also Dell often doesn't list correct memory capacity. Crucial.com is good for capacity limits but they can miss speed ratings sometimes. If you have 8GB capacity then 2-2GB ram would work. If you can't get them in the correct slots they wont be able to "take turns" processing data. I'd suggest looking at any capacitors with an X, or K scribed in the top (designed to release pressure). If the top is pushed up, or discolored you have a bad capacitor(s). They can also leak out the bottom. A television repair shop should be able to fix them. The advantage of repair vs. replace is you don't have to deal with Microsoft thinking your OS is on a new computer and want you to buy a new license. Although old Dell MBs can be real cheap.
 
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