If it literally dissapeared within a min or so it was prob just the fluid soaking through but if you've done the test a bit early a positive result if often a very faint line, sometimes barely visible but it normally stays on there. I had this problem when I got pregnant. I got the clearblue digital tests and did two of them because I was convinced I was pregnant. They both said negative on the screen and I took it that I wasn't pregnant as they both had the same result. It wasn't until later, when I went to throw the test away and I pulled the stick out of the digital bit of the test I saw a VERY faint blue line on both of them, like the original clearblue tests. If there is two blue lines, no matter how faint then it has to be positive as there is nothing else that can cause that reaction in the test other than a very rare form of tumour so I went to the nurse the next day and she confirmed it. I still have the tests and you can still see both blue lines though so they shouldn't go away if its possitive.