I have my balance cash display on my Multibit account at left top of my account which was my last transaction. But to send it out to another bitcoin account, it keeps telling me that "The wallet password is incorrect." I am fully sure, I have never changed my password and I have tried the directory given but I couldn't get it done, even none of my old transactions are showing up again. Do password regenerate itself to give new one or is my account file corrupt?

Because I know that I run some program into my computer recently i.e. photoshop program, could that be the cause? But I never tampered with bitcoin file - that is what I just can't figure out here. Please help. I am using MultiBit version 0.5.18 in Windows 7 Ultimate please help. Or is there anything else for me to try that I have not done?