Just some rules of thumb.
1. Always Install hardware using the Built-in Administrator Account.
2. Don't keep trying to re- install software that fails to install - It will leave the registry in a mess.
3. If something fails, find out WHY and don't keep installing different programs on
top of each other "hoping for success".
4. Turn OFF any AVs and Disable the firewall plus Reboot before installing any local hardware.
5. Call the Printer Manufacturer and / or the OEM Computer Manufacturer for Support if the drivers fail to install properly.
The drivers are all proprietary. :(
"Dell Tower MT 560" is not very descriptive of all the electronic hardware that might be on the USB Bus so is hard to venture even a guess as to what is going on. Also is important to know what Edition of Win7 is on the machine along with the other Software you are running which might conflict.