### See sage-5.10 folder but get no such file or directory message

I have installed sage-5.10 in my laptop with Ubuntu 13.04. The folder with sage-5.10 is there, clicking in the folder I can see all the folders and files inside it on any level. Have being using a worksheet for a while with some calculations. I start my sage worksheet in my terminal changing ~~directory:~~directory

cd /home/alien/Desktop/Sage/sage-5.10

then

./sage

then

notebook()

But suddenly when making the cd /home/alien/Desktop/Sage/sage-5.10 I'm getting the message "No such file or directory". So can't start again sage and using my worksheet. How can I solve this problem?.