Hi i have a laptop HP Pavilion Ze4500 it is coming up with operating system not found? I know nothing about computers and this just happened one day. Any one who can help i would really appreciate it, My friend tried to change the hard drive and it made no difference help me please.............. Cheers Andrea

If you have changed the hard drive, you have to install your OS again - otherwise you might be able to repair the old one.

Since you didn't write what Operating system you had, I can't guide you any further than, boot from your original OS install disk, and follow the instructions on the screen, depending on which of the above situations are true.

good luck :)

have you tried to boot-up in "safemode" by pressing the F8 key or what ever key that get you in safe mode and logon that way.

if you can then check your "msconfig" and see what services are running and what program is starting up during boot-up.

Here is another option.

The BIOS hasn't detected the hard drive

-You have an incorrect Master Boot Record

-The hard drive itself is damaged

-One of your partitions is marked as 'active' when it shouldn't be

-The partition containing the Master Boot record is no longer set as Active

Those are the general causes of the problem but how do you get your pc up and running again.

1. The first line of defense is the BIOS (Basic Input/Output System)

2. Reboot your PC and, at the appropriate time, tap the Del key or whatever key your pc requires to enter the BIOS.

3. Check in the Standard CMOS Setup that your hard drive is listed.

4. Assuming your Hard Drive is listed then you can rule out the BIOS as being the problem.

5. If it isn't listed in the BIOS you will need to check your PC manual to see what settings you need to alter to auto-detect the hard drive. If this fails you may need to manually insert the hard drive settings.

6. Once you have ruled out the BIOS you should start to look at the Master Boot Record. Insert your XP CD into the CD-ROM and allow setup to begin. At the Welcome to Setup screen press 'R' to open the Recovery Console. This is a command line interface. You will need to select which operating system you are using from the available list and then insert your administrator password. If you are using XP Home then ignore the administrator password (unless you have set one yourself) and simply press Enter.

7. Recovery Console will now run

8. At the command prompt type: fixmbr and press Enter

9. If fixing the Master Boot Record doesn't do the trick it may be worth checking to see if the partition that windows is installed on is actually Active. Obviously, if you only have one partition on your system and that contains Windows XP then that will, naturally, be set as the active partition. This option is more for those users with dual boot systems where you have an operating system on drive C: and drive D: If you have used a third party application, such as Partition Magic to create a partition you may have inadvertently made the D drive active thus cutting off the C: drive which contains the start up files. A quick way of finding out is to try booting up with an Emergency Start-Up Disk. If you can boot up with the Start-up disk go to Control Panel and click the Administrative Tools Icon followed by the Computer Management icon. When the Computer Management window opens click the Disk Management option on the left of the disk management pane. In the disk management window - lower half - make sure that the C: drive say's 'Healthy System' Also, if you can boot from an Emergency Start Up Disk you know your hard drive hasn't expired.

10. If you can start you machine with an Emergency Start Up Disk go to Control Panel, click on Administrative Tools followed by Computer Management. Finally the click the Disk Management option. Now right click on the drive you want to make Active and select 'Mark partition as active' from the drop down menu. Alternatively, if you have a copy of Partition Magic you can use this to actually reset the correct partition as the Active system drive.

11. If none of the above rectify the problem it is, unfortunately, safe to say that your hard drive is on it's last legs and is in need of replacement.