I am using a desktop computer with the below configuration
MS Windows XP Home SP3
Intel Core2 Duo,CPU [email protected],3.0GB RAM,Intel G45/G43 Express Chipset

I used the computer only a few hours ago and shut down normally, but now on power on It does not boot to windows but shows the following message
"REBOOT AND SELECT PROPER BOOT DEVICE OR INSERT BOOT MEDIA IN SELECTED BOOT DEVICE AND PRESS A KEY"

please advise what should be done. I don't have a bootable CD. I have the original Windows xp home Cd however.

Is your BIOS set to boot from your hard drive?
http://pcsupport.about.com/od/fixtheproblem/ss/bootorderchange.htm
Make sure the Hard Drive is set at the primary boot device.

If you can't find an entry for "Hard Drive" and "Reboot....Press A Key" shows up, try RESETTING your CMOS. Same error? That's because your motherboard isn't detecting your hard drive. Try doing some SIMPLE things first to ensure it still works, such as swapping cables, plugging the hard drive into a different SATA port/different IDE connector, plugging it into a different 4-Pin Molex/SATA power connector from the power supply, ETC.