Sir i have hp compaq cq40 laptop having win xp .it got effected by some virus . whenever i try to boot it it gives error in some blue screen nd stops processing without booting up windows

Did you just install a new program or a piece of hardware, update a driver, install an update, etc.? If so, there's a very good chance that the change you made caused the BSOD:
Startup using Last Known Good Configuration to undo recent registry and driver changes.
Use System Restore to undo recent system changes.
Roll Back device driver to version prior to your driver update.

Scan your computer for viruses. Some viruses can cause a Blue Screen of Death, especially ones that infect the master boot record (MBR) or boot sector.

Update drivers for your hardware. Most Blue Screens of Death are hardware or driver related so updated drivers could fix the cause of the STOP error.

Return hardware settings to default in Device Manager. Unless you have a specific reason to do so,the system resources that an individual piece of hardware is configured to use in Device Manager should be set to default. Non-default hardware settings have been known to cause a Blue Screen of Death.

Return BIOS settings to their default levels. An overclocked or misconfigured BIOS can cause all sorts of random issues, including BSODs.

If this doesn't helps you then simply get the system utility program like PC Fresher that will fix windows errors that cause of blue screen

A) Installing same version of Windows, or a lesser version;

Enter BIOS Setup, and in Boot Options, set the first boot device to CDROM.

{Windows doesn't like being copied over by the same version, or a lesser version.
The above will make the computer boot up from the Windows XP sp3 disk you have}

B) If your computer came with a version of Win Vista, and you are trying to install WinXP over it, reply in a Comment.

For additional questions please post in a Comment

Regards,
joecoolvette

Hello good day,sir
My compaq presario cq40..is powering on but blank on the screen and caps lock and num lock blingking only.I try ready so many time but everything are not meaning for me that's why i need your help,sir.please,give me some advice for power back.
Thank sir.

You need to integrate the SATA drivers for your computer in the XP installation CD using the nLite program.

Follow this guide:
http://news.softpedia.com/news/Install-Windows-XP-On-SATA-Without-a-Floppy-F6-47807.shtml

Compaq cq40 317tu vga driver. Just click the link and download your VGA driver; http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?os=2093&lc=en&cc=us&dlc=en&sw_lang=&product=3870910
Good Luck!

you mean you need to downgrade your computer from Windows Vista to XP?
if so is the case, you need to go to the BIOS in the Boot menu, select IDE from ACPI.
put the boot option to boot from CD first or disable Boot from hard disk.
then you will be able to downgrade your computer from Vista to XP.

This could be a virus, but try reloading the drivers from HP at
http://h20000.www2.hp.com/bizsupport/TechSupport/ProductList.jsp?lang=en&cc=us&taskId=135&prodTypeId=321957&prodSeriesId=432985
It the problem does not go away after loading the CD-ROM drive, let me know and we'll discuss the next steps.

i m not able to install windows xp on my compaq cq60 104tu laptop
when i boot the cd the exatrating process work properly and after extraction of all file when windows is startup a blue screen appears and
and message displayed in the screen check ur hard disk for vireuses
and installation stop

have an compaq presario cq40-301tu laptop want to load xp already vista is loaded in that while installing xp i get an blue dump error & no setting in bios found to make sata compatible please give me the solution how i can install win xp2-

hi buddy! 
follow this link for ur laptop drivers for windows xp or Vista: http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?product=3805668&lc=en&cc=us&dlc=en&submit.y=5&submit.x=6〈=en&cc=us
so it do exists. i didnt understand its not accepting win xp and vista! any way try to get a Windows Vista CD and install it. it should go fine. if not let me know we can fix it togather.
cheers suraj