If your main Hard disk is full, here’s a great little free app to help you see what’s using up the space. It’s called OmniDiskSweeper. If you are a beginner this article might be better for you, but for advanced users, OmniDiskSweeper is better – it shows hidden files.
You can download OmniDiskSweeper from here:
It does a similar job to ‘Disk Inventory’ (see here) – it shows you disk usage and what files are using the most space. The difference is that OmniDiskSweeper shows you the hidden files as well, and sorts them to show you the largest ones first. This is great as the culprits might be virtual memory swap files etc. (Which by the way you can’t delete – but you might need a larger hard drive!).