If this computer is some brand computer (HP, Compaq, Dell, ...) then give us the brand and model.
What drive does chkdsk check ? Is it the c: volume ?
If you have the XP CD then insert the CD, enter the BIOS to change the boot order priority to CD-rom first, boot on the CD and press 'R' to access the recovery console. Run chkdsk c: /R there. Wait for the scan to complete and retry to start normally. When the screen gets black wait for 5-10 minutes before turning the computer off.
Repeatedly press F8 when the computer starts and try the last known good configuration or safe mode with command prompt. If one of these options works then stop and report here.
If you can't boot into windows at all then let's rule out some hardware problem first : can you enter the BIOS at startup (press del or look for some "press xx to enter setup" message) ? Search for the hardware monitor or pc health & status screen. Report your temps, fan speeds and voltages from there.
Open the computer case and check that there's no dust. If it's dusty clean the heatsinks and fans with a can of compressed air. Restart the computer and check that all the fans are spinning (cpu fan, video card fan and rear power supply fan).
Check that all the cables are hooked properly. Look on the sticker that's on the hard drive to find it's brand and model, create the related
HDD diagnostic utility CD (DOS bootable version), boot the computer on it and run the long/extended test. Report if it finds any error on the drive.
Have you updated that computer to SP3 ? After installing SP3 did you restart the computer and did it boot properly ?
If all is fine then a repair installation of windows may be in order. If this is a retail installation then you'll have to create a
slipstreamed SP3 XP CD and
uninstall internet explorer 7 before doing the repair installation. If this is an OEM installation and you only have recovery disks then tell us about it.