I made a video showing you what is going on.
last year in 2017 when i first edited with vegas 15.0 nothing was wrong. then i updated it when a patch came out and nothing was showing up! My tracks where gone and preview screen wasnt showing up eather. so i got back to vegas 15 release version. The strange part was that when i added : Color corrector, brightness and contrast or chromakeyer over it, the preview screen doesnt show the effect. it is only with those 3 effects. color curves works fine, masking and pan crop all works fine.
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Product
Vegas pro 15.0 (build 177)
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Hardware
Lenovo : legion Y520
GPU : GeForce GTX 1050
Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
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Operating system : windows 10
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I hope you guys can help. I dont want to update because that makes my vegas go crazy. If you need any more information feel free to ask. (dont ask me for a date though XD )