Did you flash from A10 to A24 last night in one step before shut down? If it booted only once to windows last night before shut down, then could not boot any more speaks of cmos corruption.  Dell’s procedure of clear cmos is not self consistent.  Try not to plug in any power cord when you move the blue jumper to RTCRST.  Try disconnect power cord, drain all flea power, then clear cmos via jumper.  If still no post, remove all memory sticks.  Does pc beep when powered on?  No beep is a bad sign. PS a quantum leap in bios flash is risky (A10->A24).  take small incremental steps, or do not flash bios unless you absolutely need to.
Hi all, As above, I have a Dell Optiplex 990 SFF with the strangest issue. It simply will not boot, it keeps throwing blue power button and 1 and 3 glowing orange. Here are all the steps I have followed till now: 1: It initially booted fine, it has two identical Samsung DDR3 10600 4 GB RAM modules ( Model number M378B5273DH0-CH9) in it, in DIMM slots 1 and 2. I have tested these in another PC and they seem to be working fine. 2: I first noticed it had an old BIOS, A03, so I upgraded, first to A05 as per the Dell website, then to A10, also as per the Dell website, then to A24. All upgrades went smoothly with no issues. PC booted into Windows 10 with no problems whatsoever. 3: I shut down the PC last night, went to bed. When I woke up this morning, I powered on and got the issue, blue power light, 1 and 3 glowing orange. So I powered off, removed and reseated the RAM modules, still the same. 4: Removed the CMOS battery, left it for about an hour with no power cable plugged in, then replaced CMOS battery with a new one, inserted into the motherboard, plugged in power supply and powered on, same issue. 5: I then removed CMOS battery again, cleared the CMOS with the blue jumper, left it plugged in for a while to ensure the CMOS was cleared. Removed power cable, moved jumper back to original pins, reseated CMOS battery, plugged power cable back in, still the same issue. So now I am at a loss. Does anyone have any other possible suggestions I could try please? Thanking you, Mark.  
Dell Optiplex 990 SFF weird issue