Perhaps the new power supply is bad as well, can happen.
Anyway though, if your motherboards bios up to date? I wonder if it could be resolved by updating the bios to the latest version?
http://www.dell.com/support/home/us/...&categoryId=BI
Hi andrew129260, thanks for replying. I can still test the new power supply. It will give me a chance to play with my new tester. I have already updated the bios to the latest version- that was one of the first things I tried. It could be the video driver- but i've tried three versions, the native driver used during Windows installation, the one retrieved via Windows Update, and a Windows 7 driver direct from Intel for the chipset in this computer. I am running out of ideas; any more thoughts are certainly appreciated.
This is an ooold thread, but since you done a LOT already i just have to post this just in case,
and because you have all my sympathy ..
Ran into this (755)broblem myself recently and found tons of posts of the matter through the net.
Note .. my system runs on Linux (really) and the broblem appears regardless the Os!
Dont boter to change it, it wont help.
Found out interesting thought which is in the link, you should check it !
OptiPlex 755 mysteriously turns itself on - Desktop General Hardware - Desktop - Dell Community
( incase of badlink I copy the most relevant answer )
" Posted by sirihi on 18 Mar 2009 8:50 AM
OK. I had this rather annoying problem on a 755 i bought off ebay running WinXP. I'm using the latest BIOS version. The cause of this problem is nothing to do with OS version or the wake-on-lan in either the bios or in the OS settings. It is caused by the Intel AMT (active management technology) built into the motherboard. You can google this to find out about it, but essentially it allows remote lights-out management. By default it seems to be activated with it's own WOL settings enabled. The simplest thing to do (unless you want to delve in to this feature) is to simply disable it. When the dell switches on you should see an option to enter the MEBx bios by pressing CTRL + P (you'll see it in the top right hand corner of your screen). This is a separate BIOS from the normal one. Once you're in this the first thing to do is to set a password - not that simple because it is ultra fussy about the strength - it has to contain caps, lowercase, numbers and a symbol such as an exclamation mark (underscore doesn't count!). Once you've done that there is an option in the menu to simply disable the whole IAMT feature. This will stop the "mysterious" wake-up's! If you want further info on the MEBx bios features, just search!
Hope this helps! "
Alright, I will finally slay this stupid problem- the problem lies within the integrated LAN device- it is simply not fully compatible with Windows 7. In my case, it is the Intel Gigabit adapter, I believe. I turned it off in the BIOS settings. Then, I purchased a Wireless LAN adapter, that was fully compatible with Windows 7, and after installing everything and restarting, the problem vanished. It has been almost a year, and the problem has not resurfaced. THUS, there is the answer.
babyWin, that may also explain the problems you are having with Linux, though having run Linux myself for many years, I have never run into that problem. My suggestion is to buy a wireless LAN, and if you don't have one, buy a wireless router to go with it, this might fix your problem's with Linux. Are you also using the latest release of your distro, because a more mature kernel may have an updated driver that could fix your problems? Thank you for your sympathy, and for sharing the information- but all is good now! If you need more help, feel free to start a new thread, and we would be glad to assist you! Again, thanks. Take care.
Last edited by bildrk; 04 Mar 2015 at 17:59.
I agree with bybywin. I have 4 Optiplex 755's in my house experiencing problems. They mostly run Windows 7 64bit Ultimate (some have 32 bit). The problems vary by machine. They include random reboot, random power off and occasionally a mysterious power on/off. At first, before it started happening on all the machines, I was thinking it was a problem with power a supply, motherboard, a driver, Windows image, etc... Then I found the MbEX problem described on youtube. I have tried the MbEX solution and it seems to work. I will repost once this has been running long enough to be totally sure.
i know this is an old post but i wanted to let you know what i determined. in my case it is a hardware issue NOT a windows issue. i had this issue a few weeks ago on a different pc and could not figure it out. i eventually tossed the pc after swapping lots of parts. when i had the second one pop up yesterday i thought i should take a closer look. it also presented with some corrupt files so i replace the drive. then when the problem persisted i removed one ram chip at a time. removing the second seemed to work so i created the proper userid and copied files etc. then i popped the cover back on. sure enough after 2-3 minutes more crashing. i did not want to believe it so i let it reboot several more times. then it hit me. it only reboots itself with the cover ON. after more testing with the cover On and Off I determined it is a problem caused by that cover being On. So i left the cover Off.
If it works without the cover, it seems you're achieving CPU high temperatures.
To protect it self, CPU shuts down when it reaches high temperatures.
Install a hardware monitor. My suggestion is Open hardware monitor. Open Hardware Monitor - Core temp, fan speed and voltages in a free software gadget
If the CPU temperature goes higher than 80ºC, shut down and remove the fan and heat sink and clean it with a paint brush and a vacuum cleaner. Clean and replace the thermal paste.
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