help arduino mega 2560

Hello.I have an arduino mega brough on february this year.
It works fine.
This week i tried arduino 1.0 platform but i reback to 023.
After i upload old sketch , after i start again my windows 7 64 bits( i tried on 2 computers) and i want to upload new modification i received error messages(are the same on 2 computers).My arduino is ok in device manager.i tried to reinstal with arduino/drivers but i have the same error.I installed new version of java , i copy new file to java/extension like i saw in other tutorial/topics, but nothing.Please tell me what can i do?
Can be from some windows 7 updates?
Thanks a lot.

what are the specific error messages you are getting?

Many thanks.
I tried with all platform 1.0 , 023 , 022 but it is the same error.
This is what happen:

Binary sketch size: 1506 bytes (of a 258048 byte maximum)
processing.app.SerialException: Serial port 'COM5' already in use. Try quiting any programs that may be using it.
at processing.app.Serial.(Serial.java:144)
at processing.app.Serial.(Serial.java:76)
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:75)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:93)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:56)
at processing.app.Sketch.upload(Sketch.java:1603)
at processing.app.Sketch.exportApplet(Sketch.java:1568)
at processing.app.Sketch.exportApplet(Sketch.java:1524)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2293)
at java.lang.Thread.run(Thread.java:619)
processing.app.debug.RunnerException: Serial port 'COM5' already in use. Try quiting any programs that may be using it.
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:99)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:93)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:56)
at processing.app.Sketch.upload(Sketch.java:1603)
at processing.app.Sketch.exportApplet(Sketch.java:1568)
at processing.app.Sketch.exportApplet(Sketch.java:1524)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2293)
at java.lang.Thread.run(Thread.java:619)

I've been seeing a similar problem with a mega 2560 and it's driving me nuts. I'm going to try scoping the serial lines this weekend to see what's up.

Loop-back tests aren't working for me (jump D0 and D1). Do they work for you?

Hello.
I upgrade my arduinio mega to rev001(put in dfu mode and load hex file with flip 3.4.5), because i think this is the problem, but nothing changed.
I installed a virtual machine with win xp and there i put arduino 023 platform and its driver for my mega 2560.In my win7 64 bits i have my arduino on com 13 and in virtual machine on com3.In win 7 i received com port is in use and in the same time on virtual machine i can upload the sketch.After upload in virtual machine for one time i can upload on my win 7.
It is a very very strange thing.
i install last java , last .net framework...........but nothing.
Thanks and if you ave any sugestions please tell me.