The BIOS of your PC is still seeing the old settings of both drives. You will need to change these. You had two drives, your old Maxtor was disk O ,the new one was disk 1. As you have removed the old disk and I take it moved the new cloned one to its position the PC is still looking to the orignal disk settings.
Enter the Bios, I believe F12 is the key to press at startup on Dells,go to the hard drive settings and change the settings to reflect the new setup.