PC won't POST and can't enter BIOS

Question

So I have a Optiplex 990 and one day windows asked for a update and all went as usual until restart then the PC wouldn't POST and can't enter BIOS. I suppose it was a coincidence that it happened then. When I let the PC load without touching anything it starts loading and it gets stuck at the end and 1,2 led lights are lit. If I try entering bios or one time boot menu I just get a black screen with a blinking white line but the 1,3,4 lights are lit. I tried resetting the BIOS by removing the motherboard battery for 1-5 min, removed the GPU and tried on integrated graphics tried unplugging the RAM sticks one by one and removing the SSD and HDD. Nothing worked so far. And all of the hardware worked ok until now. I have changed some setting like what CPU core are used virtualization and Intel Turbo Boost but nothing too serious.

JOcean · Accepted Answer

Both of those LED codes point toward a system board failure. You can try replacing the CMOS battery as that system is approaching 10 years old and the battery may be weak. As per the service manual that battery is a CR2032. If that does not help then a system board has probably failed. And with a machine of that age an upgrade to a new far more powerful system may be the better choice.

redxps630 · Answer

remove all ram and install only one ram in DIMM1.

try clear cmos after replacing cmos battery with a new one.

assuming your 990 is MT, system board has these pins:

Password clear jumper one 2-pin connector
RTC reset jumper one 2-pin connector

move password jumper to RTC reset pins for 10 sec, then move back to password pins.

OptiPlex 990 Service Manual (Mini-Tower) (dell.com)

HPToshiba2Acer3Dell · Answer

@redxps630​ remove all ram and install only one ram in DIMM1. try clear cmos after replacing cmos battery with a new one. assuming your 990 is MT, system board has these pins: Password clear jumper one 2-pin connectorRTC reset jumper one 2-pin connector move password jumper to RTC reset pins for 10 sec, then move back to password pins. OptiPlex 990 Service Manual (Mini-Tower) (dell.com) Recently I located a OptiPlex 960. It was dusty so I cleaned it and I cleaned the fan. It did not start. Add more RAMs. It did not start. Only an orange LED on the motherboard lit. So I follow your advices here. I remove the DVD-ROMs from SATA. remove the BIOS battery for about 10 seconds. And put the same battery back.  It did not start. unplug the power. Press the switch for about 40 seconds to drain the power. It did not start. Then I say your reply here. Move password jumper to RTC reset pins for 10 sec, then move back to password pins. remove all ram and install only one ram in DIMM1. I used another 1Gb ram that did not come with the 960.  Then it starts, saying back fan failure, BIOS battery failure. A warning message appears indicating that the date and time is not set. HDD is fine. I may add more RAMs afterwards and try but the RAMs that came with the 960 at DIMM1 and DIMM3 The BIOS ask me to add a keyboard and mouse by USB. The 1 2 3 signal was on all the way. Here I know the BIOS battery is one of the issue. Replace the BIOS battery with a new battery and restart. It run memory test. It still say back fan failure even though the fan is running. Therefore, I think it is BIOS battery and other unknown issues. At least moving the 2 pin from password jumper to BIOS/RTC reset jumper for 10 seconds and move back works wonder. Thumb up to you because your solution to the original question help solve another.

Optiplex Desktops

PC won't POST and can't enter BIOS

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