I have upgraded ASA5510 256MB to 1G RAM.
After one day of working, ASA stop responding.
I reload the ASA, but nothing came on.
The LEDs are
Power GREEN, Status AMBER, Active AMBER, VPN GREEN, Flash OFF.
Status AMBER means you have not passed hardware diagnostics. I recommend you cycle power while connected via console and examine the power on self test output for additional information.
Opening the box back up and reseating the memory DIMM wouldn't hurt. You did use genuine Cisco memory and not a 3rd party, yes?