I have a Dell 530 quad desktop.When I start (power on) the computer it beeps once and stop booting on the Dell screen with the progress bar (Blue) half way across the field. I have measured the voltages at the HD and found 12v, 5v, and ~9v. I measured the battery at 3+v. Any ideas are gratefully accepted.
Standard debugging is to remove stuff until you get a clean boot.
I've seen hangs like this from firewire attached devices on a sony and USB hub attached external disk on HPs. Suggest you pull all the cables from you PC except mouse, keyboard and monitor. (no network, scanners, external drives, cameras, tablets, ups, hubs, etc.) Boot. Does it work? -no, bummer
Time for some basic (software went bad, not hardware) stuff
Hit the correct key to get into your bios during boot, whatever it is. Make sure the BIOS behaves OK as you look at different panels. It's a good thing if the BIOS works well. It proves a hardware problem if it doesn't. Before you exit the BIOS use the 'reset to defaults' pf key and the 'save' key. (make sure you save!) then exit. See if it boots. no, bummer.
Download a basic bootable diagnostic. There are a million out there. I use the one from the Corsair website because I needed it so often with my force 120 ssd before i gave up on that because it's USB based, however any bootable diagnostic will work. Boot the USB or CDrom. Exercise memory and disk. Do they fail? Yes -- POST. No -- everything works and no fails then onto broken windows. No -- the diagnostics hang on boot then onto broken hardware.
Broken windows: Boot the recovery partition on your system (if HP, sony, lenovo, etc.) or boot from the windows install CD. Do the various windows rebuilds that do not destroy your system and erase all data. If none work then buy an external USB attached disk that comes with bootable backup software, or buy software from Acronis, or google free backup software. I like acronis enough to buy it vs. free tiral copy. Get a clean copy of your system on the external USB then do a format install of windows. If this fails then back to HW.