Probably not the cause in your case, but worth checking anyway. SW doesn't handle files it cannot find very well or indeed consistantly; so if a file has been opened, saved as something else and the original deleted, or if a file has been opened over a network, from a computer that isn't running when you click on the File tab or press the "R" key, more often than not, it will stop responding, occasionally, it will come up with a suitable error message after a few minutes and very rarely it will work as you would wish and say it cannot find the file after a few seconds!
Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK
SW2009x64 SP4.1 Intel Core i7 2.94Ghz, 12Gb Ram, NVIDIA Quadro FX3700 Driver: 6.14.11.9100
SW2009x64 SP4.1 Intel Core 2 Duo 3.17Ghz, 8Gb Ram NVIDIA Quadro FX3700 Driver: 6.14.11.9100