when i start the computer i get an error message like "A DISK ERROR OCCURED INSERT THE SYSTEM DISKETTE AND RESTART THE SYSTEM" can some one help me to solve the problem

Corrupted master boot record, mate. You need to repair your NT 4.0 installation. You might be able to recover the installation by booting from a set of NT installation floppies. That's only if you have an ERD (emergency repair disk.) But, before you act, give some thought to the possibility of running Partition Magic, or System Commander, which will allow you to rewrite the MBR and set the partition as active without having to reinstall anything. The DOS version of Partition Magic can be run from a 2-floppy set without first having to perform any brain surgery on your hard drive. There are other utilities that will allow you to access the MBR from a DOS prompt, but it's been a long time since I've used them. I vaguely recall that there's an undocumented FDISK switch --> FDISK /MBR but I'm being presumptious in guessing that you might have a FAT partition on your hdd. Chances are you do not.

You may need to repair the boot sector. If you boot from NT install CD (or the 3 boot floppies) and choose repair option - even without an ERD, it will try to find your installation & repair info (its saved on the hard drive too). If it does, you'll gett he repair options - just check the boot sector repair one. Alternatively, if you're a 2k or XP install CD, you can run their recovery console (works with NT too) - then run fixboot x: - where x: is NT boot drive (probably C:). If you haven't got a CD, you can download the 4 floppy disks you need to start 2k install/recovery console from www.bootdisk.com/bootdisk.htm & get into recovery console that way (you'll need Administrator password - probably).