D630...I supported a fleet of D-series laptops as a summer job. The flashing light on the AC power adapter "brick" indicates that the adapter either is being overloaded by a bad laptop, or the adapter is defective. I saw a D620 die in this manner (dead w/ flashing AC adapter), and it was motherboard failure.
Test everything without the battery installed! Exploding Li-On batteries are not fun.
First question is whether the AC adapter light flashes when not connected to the laptop. If it does, replace the adapter.
If not, remove HDD and RAM (sounds like you've done this). If it has the Wifi card, remove that also. If all parts are out and it continues to have a flashing power adapter, try another adapter. The adapter should be 19.5V, with I believe an 85W, or 90W rating.
If no difference, it needs a motherboard. If you don't want to buy a new laptop, it's probably a better deal to buy a used D630 with no HDD on eBay and just put your current HDD in it, than it is to repair the existing one.