I suspect your problem is related to the USB driver for the onboard USB blaster. (What OS are you running?)
Try launching Quartus II and open the programmer (Tools/Programmer). Click on Hardware Setup. If you don't see the USB blaster under the "Available hardware items:" then either your board is incorrectly connected to the PC or the driver is missing/not installed properly. If you connect power to the DE2-70, turn it on, and then connect the USB cable, Windows will either ask report it found the USB Blaster or ask about installing the drivers.
If this all checks out perfectly, then we'll have to dig deeper.
Tommy