Have an Optiplex 755 PC, while working and connected to network the screen on monitor started to blink and scramble image, then the screen went black, It seemed that the machine started to restart, I saw a portion of what looked like the initial start up screen [bios yada yada] but the machine never completed starting up. I pressed the power button and held for about for about 15 seconds intending to turn the unit off, then I would try to power up again. When I attempted to start the unit, I would hear the familiar whine like it's about to start, the CD/DVD tray light near the door blinked, I hear the fan inside on, but it does not boot up anything. It does not appear to be an issue with the monitor as I switched different monitors. There are green lights illuminated on front of unit in the bar just above the power button, there is some sort of symbol lit, then a "3" and a "4" are also lit. I tried to turn off power, but when I depress the power button it does not shut down, I tried holding the power button for 30 seconds, but the unit comes on, with the normal whine noise, without booting up the system though. I unplugged the power source at the back of the unit and left it off for a couple minutes. When I plugged to power cord back in, the same things happens again, I hear the start up whine, the cd player blinks once, the same 3 lights on the bar in front illuminate, but the system does not boot up.
Take out all the ram and try to turn it on. It should beep.
3 4 Lit means BAD RAM.
Then put 1 stick of ram back in at a time to see which one is bad.
Thanks Speedstep... I removed all RAM sticks [4 each 1 gig] then plugged it in and turned on.. it didn't "beep" was more of a buzz, so I disconnected power again, I started inserting RAM sticks one by one, starting from top down, I tried all 4 sticks individually and each time I would get different indicator light error of "123" which I searched and found out that mean "other error" So with each stick not working I decided to do the same process in different slot. Eventually through trial and error, I found that DIM slots 1 and 2 work, but any RAM stick in DIM 3 or 4 give the error indicator lights "123" I am by no means computer savvy, but I *think* it's a problem with the slots in the motherboard? identified as DIM 3, DIM 4. ?
So I now have half of the RAM I used to [2 GB instead of 4 GB] I installed all peripherals again and plugged into power and started computer, it booted up but I had to start in safe mode because widows wouldn't start, it did a check and made some repairs and eventually after restarting Windows came up. There is a noticeable difference with less RAM.
I am wondering if worth it to try to repair the other DIM slots? I presume would need to replace mother board? [is that fairly easy?]
So yes it was a RAM problem, not in the RAM sticks themselves but the ports they plug into.
8 gigs is an option so you could get 2 new guaranteed to work in 755 ram sticks and get back to 4. However the prices on Ram make this good money after bad.
You can Get Dell Precision T3500's which have 6 DDR3 ram slots and take up to 24 gigs of ram cheap.