Flush the disk caches. And by all means learn how to save incrementally and use backups. If the project is genuinely damaged and flushing the caches doesn't fix it, you could find yourself in a very dark place without an alternative to go back to...
First I apologise for my poor english, see it is not my native language.
Now, I have tried that and it didn´t do me any good.
I have backups, however Im not sure if "save incrementally" means the same thing.
Plus, I have managed to RAM preview going by parts, however I don´t feel like that must be the only way to do it.
What exact version number of After Effects are you using?
I am using version 188.8.131.52.
Is not my computer enough to run After Effects?
I can work on the project but I just can not preview it to see the full picture, and this is slowing the process by a lot.