This is HP's suggestions:
The Computer Will Not Startup or Boot, Displaying a Blinking Cursor
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Windows may not startup or boot. The notebook will stop responding at a black screen with a blinking cursor in the upper left corner of the display when attempting boot Windows XP O/S.
This behavior can occur when your PC is attempting to boot from a bootable storage device such as a USB or 1394 (Firewire) hard drive, optical media (CD or DVD) or a flash memory card. Another possibility, is the hard drive may be damaged. Use the options below to diagnose and resolve the problem:
Option 1: Remove Devices and Reset BIOS Defaults
Remove all external devices and media. Be sure to check the optical drive, flash memory slot and the floppy drive (if available).
Restart the computer by holding down the Power button for 5 seconds. Then release the Power button and press it again briefly to turn the computer on.
When the power light turns on, press the F10 key on the keyboard to enter the system BIOS menu.
Press the F9 key to reset the BIOS defaults. Then Press the F10 Key to save the changes and restart the computer. Press the Enter key when prompted to save the changes.
If after performing steps 1-4 Windows does not startup properly, then the hard drive needs to be tested using the following steps.
Option 2: Test the Hard Drive
Use the steps below to test the hard drive in a Notebook PC using the HP Hard Drive Self Test.
Plug the AC Adapter into the Notebook PC.
Press and hold the Power button for 5 Seconds to turn off the PC.
Press and hold the F10 key. Then Press the Power button to turn on the PC releasing the F10 key after text is displayed on the screen of the PC.
After the BIOS Setup Utility is displayed, use the Right Arrow key to select the Tools menu.
Select Hard Drive Self Test
Press the Enter key to start the test.
The Hard Drive Self Test will provide an Estimated test time . A Quick test a Comprehensive test and a SMART test will execute when the Enter key is pressed.
If any test fails , contact HP service and support for instructions on how to order a replacement hard drive.
If all of the tests pass, the hard drive is not damaged. As a rule, HP will not replace a hard drive under warranty that does not fail the HP Hard Drive Self Test.
NOTE: Many PC problems are related to soft failures on the hard drive. The comprehensive portion of the HP Hard Drive Self Test will repair soft errors on the hard drive, but it will not report the errors. After the test is complete, be sure to restart the PC to see if test repaired the problem you may be experiencing with your PC.
If none of the above options correct the problem, please contact HP service and support to schedule a repair.
Option 3: Reseating the RAM
Reseating the RAM may resolve this issue. On most notebook PCs, removing and reinserting the memory is a simple step and does not require advanced technical knowledge of the computer. HP recommends reseating the memory module before arranging for warranty service repair. If you are not confident following the steps for removing and replacing the memory module in this document, contact an HP support specialist for assistance.
NOTE: If someone other than HP installs or upgrades the RAM, any damage caused by the RAM and/or by the person when trying to install or upgrade the RAM is excluded from coverage under the product warranty. The customer assumes all risk and liability for damages for any such installation or upgrade.
NOTE: Some HP notebooks may have a secondary memory module located under the keyboard. For removal and replacement instructions pertaining to the second memory module contact HP service and support.
Use the following steps to remove and replace the memory modules:
WARNING: This product contains components that are easily damaged by Electrostatic Discharge (ESD). To reduce the chance of ESD damage, work over a non-carpeted floor, use a static dissipative work surface (like a conductive foam pad), and wear an ESD wrist strap that is connected to a grounded surface, like the metal frame of a PC.
Step 1 - Remove the battery
Slide and hold the battery release latch to the unlock position.
Use your finger to lift the battery up and out.
Step 2 - Remove the memory module
Locate the memory module cover on the bottom of the notebook.
Remove the screw that covers the memory module.
Use your finger or a flat head screw driver to lift the inside edge of the memory module and remove it.
Push both tabs outward simultaneously to release the memory module.
Grasp the memory module by the edges and pull gently to remove it.
After removing one module, replace the memory expansion cover and then replace the screw.
Step 3 - Replace the battery
Insert the battery into the notebook.
Push the battery into the base enclosure until you hear a click.
Connect the AC adapter and turn on the notebook.
NOTE: If the PC will not start up and you experience another failure not covered in this article, view the documents in Related Links for further information.
After the memory is reseated, connect the AC adapter and turn on the notebook:
If the notebook boots normally and the Windows desktop appears no further action is needed. If this problem re-occurs often, contact an HP Support Specialist to schedule a repair.
If the notebook continues to stop responding at the Compaq or HP logo, turn off the notebook continue to the next section of this document.
Option 4: Hard Reset
Forcing the notebook to reboot may resolve the issue.
Press and hold the power button until the notebook powers off.
Press the power button again to boot the computer.
If the options above do not resolve the issue, performing a system recovery may be necessary. View the documents in Related Links for further information.