2000 subaru forester wont start battery is good what can I check next

Ignition switch first then look for the ignition relay under the hood.

you need to check for fuel pressure next.
Could be many things, but a fuel pump or fuel pressure regulator would be prime suspects.

Changed battery now running lights flash 2000 Forester Quick fix on mine use remote key fob lock door then unlock everything good no more flashing.

first have a compression test done to know for sure if head gaskets
from your description I think not as it would be overheating all the time
if you are running hot all the time and the radiator is original the cores could be blocking up so a replacement radiator would be a good move
next check out the cat converters because if they are blocking the exhaust , the hot /cold on off readings could be from them failing and blocking the exhaust

No, and add some Trans X slip stop and leak stop, sold by K and W. about 16 ounces, this really helped my Forester, as a lot of them have this issue with the clutch pack in the tranny. sold at most auto parts stores and Wal Mart. take care.

Are there any other possible problems, or you are just not receiving spark at all now?

The coilpack could be dead and just need replaced. If you have a voltmeter or a test light, check the wiring on both sides of the coilpack harness to make sure it is receiving power.
I don't believe Subaru used ignitors past '99, but if they did, your should be located on the firewall behind the throttle body. Make sure it's plugged in and receiving power.

Coil packs do go bad from time to time. I had to replace mine in my
'98 Impreza a while back.

Goodluck!

flush your heater system probably clogged with dirt the coolant shld be circulating continously going to the thermostat in which the heat is responsible for opening the thermostat to allow coolant circulation

On another forum someone said to disconnect the cables from the battery; press on the brakes several times to release any electrical charge still in the system; wait a few minutes and reconnect the battery cables. It worked like a charm--speedometer, tachometer, and display all function now!

alternator belt is off or broken,a/c uses a seperate belt

I have a 97 subaru outback and encountered the same problem. It is a security device on all newer subaru's. After changing or charging the battery, leave the negetive battery cable disconnected. Turn the key to the "on" position, then reconnect the negative terminal. This will stop the flashing.