If the DRAM LED is 'on' then upon posting the ASUS BIOS determined the RAM has a problem. The problem can originate from a few issues:
1. Incorrect DIMM slots:
1 stick: CPU: | -- | 4GB | -- | -- |
2 sticks: CPU: | -- | 2GB | -- | 2GB |
2. RAM is improperly seated in the DIMM slot, carefully remove the RAM using the release, examine both the DIMM slot(s) and Stick for problems or debris, reinsert and make certain the locking mechanism 'snaps' in to place.
3. Bad stick of RAM, if you have 2 sticks try 1 stick at a time.
4. Other issues: Bent CPU Pin(s), Grounding/Shorting: aftermarket HSF with metal backplate, or Case with punch-out 'standoff's' vs brass standoffs.
Yeah, you'll need to update the BIOS. Unfortunately, the only way to do that is with a Sandy Bridge CPU installed. If you know someone that has one that you can borrow for that, that would be perfect, but you may be able to get a shop to loan you one for that as well. As a last resort, you can buy a cheap Sandy Bridge Celeron to do it.
After you do that though, you should be good to go.