hhhheeelllppppppp pleaseeeeee!!!!!

Hi i like very mucho to fly in the fs9 but i dont know why two times, while flying from paris to mexico something very wierd happened.
I was traveling at 35,000 fts and at a cruise speed of 337IAS (that was the speed that the velocimeter was telling me, is the indicated speed, and in the gps where it says GS it was telling me 514 something normal my ETE marked in the right was telling me that i was going to arrive mexico in 9 hours, normal. But suddenly the speed in the gps began to fall. It went from 514 to 399 and imagine, the ETE became like 15 hours but the speed in the velocimeter stayed the same.
I am very desesperated because I arrive a lot more late. I dont know what to know i also dont know what is the difference between ETA and ETE and allways when i arrive mexico i am almost out of fuel is that normal? I knew that the 747 goes farest. Please i really need your help, just for the record i took out all airplanes form the folder of aircraft because the game was very slow i dont know if that has something to do with this
thank you very much for your help.
I was traveling at 35,000 fts and at a cruise speed of 337IAS (that was the speed that the velocimeter was telling me, is the indicated speed, and in the gps where it says GS it was telling me 514 something normal my ETE marked in the right was telling me that i was going to arrive mexico in 9 hours, normal. But suddenly the speed in the gps began to fall. It went from 514 to 399 and imagine, the ETE became like 15 hours but the speed in the velocimeter stayed the same.
I am very desesperated because I arrive a lot more late. I dont know what to know i also dont know what is the difference between ETA and ETE and allways when i arrive mexico i am almost out of fuel is that normal? I knew that the 747 goes farest. Please i really need your help, just for the record i took out all airplanes form the folder of aircraft because the game was very slow i dont know if that has something to do with this
thank you very much for your help.