What color are the 4 diagnostic LEDs when you see the blinking cursor? Look up the error codes here, page 139.
Dead motherboard battery and/or scambled BIOS settings? If the system was used and probably unplugged for a while, the battery may have died. So try installing a fresh 3-volt CR2032 lithium ion coin cell battery, ~$2-$3 at most discount stores. Check the manual for your specific form factor (eg, tower, desktop, small form) for instructions to change the battery.