How to install an operating system on a Dell Optiplex GX280

SOURCE: Dell Optiplex GX280 boot problem

I just repaired two Gateway systems with similar behavior (turn on power, fan runs at full speed, no boot), and both needed replacement system boards. (These were a different model, but the symptoms are typical of a dead system board.) I got the boards from a company called Blue Raven Technology (www.blueraven.com).

Before deciding the main board is bad, try another power supply to make sure that's not the problem. Also you might try clearing the CMOS memory on the system board (either by moving a jumper usually found near the backup battery, or by removing the battery itself). Sometimes corrupted CMOS data will keep the system from booting.

SOURCE: I own a Dell Optiplex

Hi 
    What Operating System was on the Machine?

SOURCE: Dell Optiplex GX150 Factory Settings Restore Partition...

This is from the Dell support site. You were correct in pressing ctrl+f11 but perhaps you did not press at the correct time. If in following these first two steps you do not get the recovery console, it may not have been installed on your computer.



1 Turn on the computer.
2 When the Dell splash screen appears during the computer startup process, press and hold <Ctrl> and then press <F11>. Then, release both keys at the same time.
3 In the Dell PC Restore by Symantec window, click Restore. Alternatively, press <Tab> to highlight Restore, and then press <Enter>.
4 When a warning message appears stating that all data will be lost, click Confirm, or press <Tab> to highlight Confirm and then press <Enter>.

The Progress window will appear. Once the restore process starts, Dell PC Restore by Symantec usually takes about 8 to 10 minutes to finish.

When the restore process is complete, the following message will appear:
The system recovery process was successful.
5 Click Finish or press <Tab> to highlight Finish and then press <Enter> to restart the computer.
The software is now installed as it was when the computer was first received.

SOURCE: dell optiplex gx280 won't boot up

you either have the boot priority in the bios off or you have improperly cabled your hard drive . perhaps you set it to boot to cd while installing the operating system and forgot to change the order back.
The floppy drive does not have to be present for the system to boot (if set to "not installed" in bios)
your boot devices are your cd/dvd rom and your harddrive.
Seeing as you've recently replaced the power supply , ime assuming you didnt dismantle the whole computer , just the power leads coming from the power supply, which means you only moved power , not data cables.
This would be the first thing to check -- power to the harddrive and cd rom, the 4 pin connector that sometimes connects to the motherboard and any data cables you might have bumped while changing the power cables. check these things and post here again.
Regards

SOURCE: Dell Optiplex GX280 Video Card Install Problem

You hit that one right on the dot.  ATI website showed the specs for that graphics card you installed as needing a 300 Watt power supply.  Good news though... I researched newegg.com and I believe I found your 300W power supply.  There are 4 different Optiplex gx280 designs with 4 completely different power supplies.  Since you bought the low-profile video card, I believe you have the slim computer case and this power supply should work for you...
http://www.newegg.com/Product/Product.aspx?Item=N82E16817374002

Good Luck