Osborne Executive will not boot.

I have an Osborne Executive which I recently got. The power supply must have failed as the person I bought it from had replaced it with a modern ATX type. Regardless, the machine boots up and gets to "insert boot diskette screen".
It did originally have boot disks but I made some from the images that I found on the web and used teledisk to transfer them. Even though the disks have no bad sectors, it will not boot to these disks. Any suggestions?

Have you cleaned the drive heads?
My first step with any drive is a floppy cleaning kit and some isopropyl.

I took it all apart yesterday to clean it and yes, the heads were clean, however, the belt must have slipped off the drive A: so I put it back on. I reassembled the machine and I got nothing on the screen. I pressed the reset button and the familiar "boot disk" screen appeared. I inserted the disk but it would not load. Instead of the light staying on solidly, it had a pattern of on off, on, off. I thought it was reading the disk but I removed the disk from the drive and pressed enter and the drive made the same pattern with the light.

Okay, I've taken it all apart and if I have the power cable removed and then pull it in and turn on the power supply a message will appear saying "Computer not working properly, contact an Osborne Dealer." In the top left hand corner of the screen it has the letter P. don't know what that signifies but it must be something. If I leave it in and turn it on with the power cable already in and powered up once already, it will not give me that screen. Anyway, pressing reset gets me to the boot screen, I've tried swapping B and A drives and it only gets me as far as "Disk is not a valid system disk". I did make sure the boot disks I had were SSDD type and there were no bad sectors.