what was the error message?and windows moves the drive letters?and MAYBE c drive is d or e now. link >http://support.microsoft.com/default.aspx?scid=kb;EN-US;q307028  have you considered this>http://www.boot-us.com/screensh.htmlook here>http://vil.nai.com/vil/content/Print926.htm if you need a fresh boot disk it can be found at www.bootdisks.com or you could try taking the hard/drive from your laptop CONNECT it to your pc as a salve and format it there if this is easier?After you install a new harddrive, the next step is the fdisk where you set up the partition (s).  The instructions to the COMPUTER which are on the startup disk, is placed in ramdrive.  The ramdrive drive is TEMPORARY and will disappear when the computer is shutdown.  But each time you use the startup floppy to start the computer, the ramdrive is setup. Most of the time it sets up as drive "d". Sometimes it sets up a drive "c".  When it calls itself drive "c", it will not let you format drive "c" as the primary drive.  What I did was to go back to fdisk, displayed the PARTITIONS (I usually assign 100% of drive to primary logical partition) to see what happened there. After I see that there is only one partition there, I exit fdisk.  Then without rebooting, at "A" prompt I format "c".  You have to format "c" before you can install the OS.  I'm having the same problem only this time i'm installing a second hard drive and the BIOS detects it but when i use fdisk to set partitions and drives it says "UNABLE to access drive 1" I have a WD caviar 40GB 7200RPM set as master and MAXTOR 20GB set as slave please help!!!!What type of OS do you install?
All the logical patitions are NTFS?
Note that "Fdisk cannot read NTFS".
Try to use other Disk Utility Such as Disk manager to check.
 
Try to install new HDD on the other IDE Connector.