System was running just fine (I had to install a new hard-drive and graphic card about a year ago, but since then all worked perfectly). As of yesterday it will not boot. I get the windows logo and a dell logo, and the option to press F2 for system settings and F12 for boot sequence. I don't know enough about either to mess with it. If I don't press either of these two, the next screen is black with a blinking underscore (cursor). Nothing happens.

Is this a hardware failure or software issue? Is there anything else I can try to fix it? The computer is otherwise a great machine.

Do you have an XP pro install disk? It sounds like some of your files may have been corrupted. Also have you tried booting in safe mode (press F8 after logo appears) Or just after machine turns on try pressing F8 and you should get the safe mode boot menu.

I don't even get to safe mode. On the black screen it just freezes. I do not have the installation disk, as this machine is my old work machine and was given to me when they upgraded all equipment at work (former job). If I have any certainty that it's software related, I'd buy XP Pro... but I want to avoid buying it and still not getting it to work. Thanks for your help

If the machine came with XP pro and you have friends that have it you can borrow it from them. Its legal so long as the machine came with it. Your boot files are corrupt.