Last night, I flew Qatar 777 from Doha heading to Dulles. I slept an upon waking up, my plane was almost near the east coast. I then started programming my arrival (STARS). While doing so, the game stopped responding and I waited for more than 20 minutes and had to cancel my flight :(

First, welcome to Avsim.

Second, you did not mention what simulator you are using, if you were using a default or add-on aircraft, and if you are using default or add-on airports, weather, and AI traffic.

If it is FSX that you are using, you may have run out of memory.  You might think that a computer with 8, 16, or 32 GB of RAM is enough, but FSX is an old sim and is a 32-bit program.  It will only use a maximum of 4 GB of RAM.  Once it has filled or nearly filled 4 GB, it will crash.  To top it off, FSX was never really efficient at releasing RAM that it no longer needed.  So as it continues to load scenery as you fly along, it does not remove scenery that you have overflown and is now far behind you.  Add in some add-on aircraft, add-on airports and weather and FSX gobbles up RAM even faster.  High autogen settings really eat up memory.  The FSX-Steam Edition is much better at managing its memory usage, but the old boxed versions of FSX were really poor at memory management.