Normally, the Dell logo screen starts followed by Windows starting up. Windows usually will try to repair itself if it does not boot the first time; and if the repair fails then you will get a message that the repair files could not fix the boot issue. Sometimes you get a beep code or the LEDs will blink in a pattern if there is a hardware issue.
If you get neither, then you should try to repair Windows with the Windows installation disk. It should give you the option to install Windows or Repair Windows, choose repair and wait to see if it can repair the boot problem.
You can press F10 when you see the Dell logo and enter diagnostics, if there is a hardware problem then this is where you will find it. F2 will take you to BIOS, you can check the hard drive setting; Raid On or AHCI are the usual settings, if the computer does not boot then switch from Raid On to AHCI or opposite if it is set that way. If changing the setting does nothing then set it back to its original setting.