By copying, I meant moving the drive from one different PC to another without reinstalling the operating system. This is effectively a copy even though the hard drive itself is moved. The reason for this is due to the hardware differences between the Dell and Toshiba computers. There are drivers and other low-level software that are modified when Windows is first installed or run, this can cause stability problems or cause Windows to think the sofware isn't genuine.
The easiest way to get Windows again is to find someone with the discs, the product key is what determines which version is installed. If you have a friend with a copy of Windows 7, you can use that install media and your product key. You will probably have to do a manual activation over the phone once installed. Alternatively, you can go to Newegg and buy a system builder copy of Windows 7 or 8 for $99 and treat that as a fresh install.
Building a PC yourself and using the system builder edition of Windows is far less expensive, but the license on that edition of Windows locks it to the motherboard. This isn't a technological limitation, but rather a licensing one. If you move Windows to another PC with a different motherboard, you can activate manually and get around it, but you are technically violating the license. This is caused by how Microsoft defines a PC, to them, a PC is based on the motherboard, so, for licensing purposes, if you change motherboards, you are using a different PC. With system builder editions, you may not have the same activated copy of Windows on two different PC's, thus, attempting to do so will cause the activation process to fail. A full, boxed retail copy of Windows may be moved from PC to PC but a manual activation may be required.