On startup, folder with question mark and finder window appears.
when i switch on the computer i get the start up chimes and the grey screen with the apple logo, this switches off very quickly and comes back on with a small folder which has an alternating question mark and a picture of the finder logo.
I have already replaced the hard drive once with another one form the same model computer and it worked for a while (two weeks), but now it has exactly the same problem. i have also reinstalled the software with no luck.
the strange thing is that sometimes it does boot perfectly and sometimes this happens right after i have just had the problem with startup?
I have run out of ideas for what to do.