HP550 lap top unable to install windows 7 from cd

[Hybrid079]

When I turn on my HP550 notebook with the Windows 7 OS disk inserted I get an error message, in the past it used to run the setup instalation process automatically, now it doesn't do it!! What could be the problem, I've did a HHD disk check & all was completed sucsessfully, I even did a Disk Sanitizer & still can't reinstall windows on it??

 

[rgd1101]

And what is the error message?

 

[Hybrid079]

And what is the error message?

 

[Hybrid079]

When I switch on the power button I get the following messages :
• Initializing Intel(R) Boot Agent GE v1.3.52.2
PXE  2.1   Build 089.2 (WfM 2.0)

» (Next Screen)

Intel(R) Boot Agent GE v1.3.52.2
Copyright (R) 1997-2010 , Intel Corporation 

Intel(R) Boot Agent,   PXE Base Code (PXE 2.1  build 089.2)
Copyright (c)  1997 - 2010,  Intel Corporation 

Initializing and Establishing Link...

» (Next Screen)

Non-System disk or disk error 
Replace and strike any key when ready.

• NB. And this screen just refreshes when any key is striked, this happens with a Windows 7 or XP Operating System CD disk is installed into the CD disk rom?.
• Please help & thank you for your reply!