I have been working an arrangement, constantly crashing on me, not enough memory, etc. and now since I redid a portion of it, it no longer exists....why

It won't load even though it trys...this is on my premium 17 music maker..,.

my computer :  AMD Athlon(tm) II4 640  processor  3.00GHz 

                           4.00GB

                          64-bit Op sym

I've looked up back up files, and previous versions  (4/21/12), but when I try to load the most recent version, it only fickers then goes empty

When I was working on the arrangement I was constantly saving because the program was constantly crashing after working on the arrangement for awhile, and I had to restart my computer in order to refresh;  I was getting messages of not enuf memory, strange noises, freeze ups, black outs, messages containg the words, "Dummy, Dummy, Dummy"; this has been going on for quite a long period of time, but whenever I submited a report, I would never get any appropriate answers, and in some instances even talked down to...

 I can't even find back up for my latest version (4/24/12), even though my records clearly states that the last save was on 4/24/12 9:46 pm

 I have run out of ideas of where to look, or how to get the arrangement to load, and all that happens is that the loading box flickers for a second then goes out..

What do I do next?