Your drive is probably formatted in the NTFS file format, which is the default choice in Windows XP. In order to use an external USB hard disk drive (HDD) with this recorder, you have to change the format to FAT32. Changing the format of an HDD is a procedure that we only recommend to experienced PC users. WARNING: Formatting your external hard disk drive will delete all files that are stored on it! Make a backup of all important information. Philips will not be liable in any way for lost or damaged data and we can not guarantee that changing the format will solve the issue. Windows XP does not support formatting any media larger than 4 GB using the FAT-32 format. Therefore, you need to download a dedicated program. One suggestion is CompuApps' SwissKnife tool (http://www.compuapps.com/download/Swissknife/swissknife.htm), but on the Internet you will find a large number of disk utilities free of charge. After you have formatted your HDD as FAT32, your recorder will be able to recognize the files that you store on it. Not all external USB hard disk drives are compatible with this recorder, so even a HDD in the FAT 32 format may not function properly.