As per my understanding you are not getting any display on the monitor.
In order to isolate this issue, I suggest you to try the following troubleshooting steps:
1. Determine if the system worked before. Determine if there have been any recent changes. Often if a recent change is been made, the recent change is the cause of the problem.
2. Check whether the monitor settings are set properly and all the connections from/to monitor is setup properly
3. Ensure that the power supply fan is spinning. Verify that the power supply has the capacity to power all the devices used in your system.
4. Make sure the power cables inside the computer are attached correctly and secure.
5. Check for any metal objects such as screws that may ground the motherboard and make sure the screws that hold the motherboard are not too tight.
6. Check and make sure BIOS jumper is on default (1-2) position.
7. Remove the processor and RAM and reinstall them to make sure that they are installed correctly.
8. Use only basic components and remove all add-in cards, floppy devices, IDE devices, and peripheral devices such as printers, network connections, USB devices, etc. Take out all unnecessary components, make sure only Processor, RAM is attached to the motherboard and try to switch on the computer. If the issue is resolved, please reconnect the detached devices one by one to isolate the faulty component. If the issue still occurs after removing the non essential components, the problem has to be with the RAM, Motherboard or Power supply
9. If the problem still persists, swap the RAM with known good RAM. In addition, test the suspected RAM in another known working system.
10. Leave the CMOS battery out of the computer for about 20 to 30 minutes and then return it to its socket or Please try with a New CMOS battery
11. Try to switch on the motherboard using another compatible power supply (if available).
12. If the problem still persists, swap the processor with a known good processor (if available). In addition, test the suspected processor in another known working system.
13. If the problem still persists, swap the motherboard with a known good motherboard (if available). In addition, test the suspected motherboard in another known working system.
14. Please refer the below mentioned URLs to get more assistance about your issue.
Please refer the link given below to check the compatible Memory and processor for DG31PR motherboard:
If the above Trouble Shooting steps fail to resolve the issue please try performing BIOS recovery if :
LED light is glowing
Processor FAN is spping
File Name: PR0071.BIO
IMPORTANT: This BIOS recovery Does Not require any display. Once you are in BIOS recovery mode, there will be no display as
the diskette is being read. The procedures and the link are provided below for your guidance.