The power light is on, but the monitor is off

This error can be caused by one or more of the below possibilities.

Floppy or CD that is not bootable is cur...
BIOS or CMOS setup is not setup properly...
Hard disk drive does not have bootable f...
The hard disk drive is bad or not connec...
Solution: Floppy or CD that is not bootable is currently in the computer Verify that no floppy diskette or CD is currently in the computer. If a diskette or CD is in the computer that is not bootable your computer may attempt to boot from that diskette or CD causing this error message.
BIOS is not setup properly Additional information and help with getting into BIOS or CMOS setup can be found on http://www.computerhope.com/issues/ch000...
Verify that your hard disk drive is setup and detected properly in BIOS. You're computer should list a hard disk drive installed either under the main page or the drives page in BIOS. If BIOS indicates the drive is not installed or not detected skip to Hard Disk drive is bad or not connected ....
Verify the boot options are properly set in BIOS, almost all BIOS setups should contain options specifying how your computer boots. For example, most computers should have their boot options setup similar to the below example.
 - Floppy drive
 - CD drive
 - Hard drive
 
Rest your BIOS to default values. Many BIOS will enable users to reset the values to the default settings. If you've tried the above options without success try resetting the BIOS.
Hard disk drive does not have bootable files on it It is possible that command.com or another bootable file may be missing from the hard disk drive. Follow the below steps to possible resolve your issue.
Windows 95, Windows 98, and Windows ME users
Boot from a bootable floppy diskette.
At the A:\> type fdisk <press enter>
If you receive a message no fixed disk present, read Hard Disk drive is bad or not connected ....
If you are able to get into fdisk, choose option 4 to display the partition information. In the partition information, if the System is listed as FAT16 or FAT32 then continue to step 5. If you have a message indicating no partitions defined, no information is on your hard disk drive and you will need to create a new partition. See our fdisk page for additional information.
If you see FAT16 or FAT32 in fdisk press the ESC key until back at the A:\>
Once at the A:\> type, sys c: <press enter> (only do this command if you are using the same operating system that this diskette was created on).
This should return a message 'System Transferred', if you receive bad command or file name and have verified you have typed the command properly, you will need to obtain a bootable diskette with the file sys.com on it.
If system was transferred successfully, reboot the computer and issue should be resolved.
Windows 2000 and Windows XP users
Boot from either your ERD, your bootable Windows CD, or your bootable restore CD.
Once boot attempt to repair Windows. If you're able to repair Windows remove the disks and reboot the computer.
All users
If your operating system is not listed above or the above steps did not resolve your issue you can also try erasing the hard disk drive and starting over.The hard disk drive is bad or not connected properly
If you have attempted all above suggestions and you are still encountering the same issues, verify the connections are properly connected to the computer if the hard drive was recently installed or the computer was moved.
Unfortunately, if all connections are setup properly and all the above recommendations have been attempted, it is likely that the hard disk drive is bad and it will need to be replaced.

Or:

Cause:
This is an expected operation. In the Boot Device priority setting in BIOS, you will see Removable Dev. (floppy), Hard Drive, ATAPI CD-ROM, and typically last is Intel® UNDI PXE 2.0. This setting will attempt to boot off a remote agent using the onboard NIC. By seeing this message it means the PC cannot find a boot partition on the floppy disk, hard drive or the CD ROM to load the operating system. Solution:
Install an operating system or put in a bootable device into the floppy or CDROM. If you do not plan to boot to a remote boot host, you may disable the Intel® UNDI PXE 2.0 option from the BIOS setup utility boot order. Relevant Information: No operating system installed
C drive does not have an operating system loaded
No bootable floppy diskette in diskette drive This applies to: Intel® Desktop Board CA810E
Intel® Desktop Board D810E2CA3
Intel® Desktop Board D810E2CB
Intel® Desktop Board D815EEA/D815EPEA
Intel® Desktop Board D815EEA2/D815EPEA2
Intel® Desktop Board D815EFV/D815EPFV
Intel® Desktop Board D820LP
Intel® Desktop Board VC820


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These products are no longer being manufactured by Intel. Additionally, Intel no longer provides interactive support for these products via telephone or e-mail, nor will Intel provide any future software updates to support new operating systems or improve compatibility with third party devices and software products.
THESE DOCUMENTS ARE PROVIDED FOR HISTORICAL REFERENCE PURPOSES ONLY AND ARE SUBJECT TO THE TERMS SET FORTH IN THE "LEGAL INFORMATION" LINK BELOW.For information on currently available Intel products, please see www.compaq.com and/or developer.qompaq.com
Comment by Beni S-P, posted on Oct 26, 2007
And i forgot :
check power suplay and ram???Let me know if u get help???