|Dell? OptiPlex? GX270 Service Manual|
Your case has a Chassis Intrusion Switch.
- The power led may blink depending on a setting regarding that switch in your bios Setup, when the case has been opened and then closed again.
- The switch may be defective, or it may have gotten displaced from where it works properly.
If it's defective usually if you disconnect it your problem goes away, but there may also be a bios setting you need to disable.
Chassis Intrusion Switch
Dell? OptiPlex? GX270 Systems User's Guide
A power supply or system board failure may have occurred.
See "Power Problems."
Did you replace the PS with an el-cheapo one?
Don't buy an el-cheapo PS.
See response 3 in this:
"...that flashing amber light which by the way stays flashing after awhile even when my power cord is disconnected..."
The power supply has large capacitors in it that store a charge - it takes a short while for them to discharge after having removed the AC power to the PS.