Can't boot past Toshiba screen. Is HD gone?

[stevewall]

I have a 3 yr old Toshiba Satellite M35X laptop. I am running XP. It has a Celeron processor and a 40GB HD. 512RAM.
Today I was surfing the web and left for a half hour coffee break. When I returned I was confronted with a black screen and the following: "Intel UNDI, PXE-2.0 blah balh. Then:
"For Realtek RTL8139(X)/8130/810XPCI
Fast Ethernet Controller N2.13 (020326)
PXE-E61: Media test failure, check cable
PXE-M0F: exiting PX ROM
Invalid partition table"

I couldn't do anything. I turned off the computer with the power button, waited five minutes, turned the computer back on and got:
The Toshiba screen, which led to a black screen with a cursor in the extreme upper left hand corner.
Then this message appeared:
"A disk read error occurred. Press ctrl+alt+del to restart" which I did.

This resulted in the Toshiba log on screen and followed by the Realtek screen again, but this time it repeated itself for ever.

What is causing this, and can it be easily remedied, or do I have a defective hard drive? (!)

Thank you, in advance, for your prompt responses, good or dire!

[socrates]

Well, invalid partition table means that it's not able to read the partition information.... could be a corrupted hard drive. 

Have you had any issues lately with the laptop?  Has it been slowing down considerably, causing issues when copying data, etc?  Also, have you had issues with it rebooting, or have you been holding down the power button to shut it off?

[squall_01]

Is there anything else that comes up?  I would go to a tech store and see if they can pull off any important data an they tell you if the drive is bad.  Does sound like your HD has been corrupted try repairing it with the xp disk if you can get into it and know how.