Mavericks accessing system drive clears screen

TThis is VERY odd, I am running Mavericks which has been working happily for many months. I can run any program by accessing it via Quicksilver shortcuts BUT if I click on the startup drive icon to open it in a window a window briefly appears and then both my screens blank out and the finder reappears after 4-5 seconds exactly as it was before I clicked on the icon. I can open any other drive and happily look in any folder without problem. I have a duplicate of my startup drive (Carbon Copy Cloner - daily) and if I restart using the copy I can access the original startup drive but now the problem is repeated on the copy and I can't open

tthat drive up....although I can run programs. Clearly I have installed something that is affecting things but what? I have tried clearing PRam, deleting preferences, anything generated in he last week.... Which I can only do by restarting using my copy startup drive) I have been a mac user now for over 25 years and am pretty savvy but this has me beaten...any ideas? It's hard to describe but if anyone wants more info please ask and I'll try to provide/describe. Here's hoping! Many thanks for taking the time to read this. Last thought in terms of description - it's almost like the finder is restarting every time I access the startup drive, but quickly.