Unity Crashes On Startup

I've got a big problem here. We're releasing on Steam in less than a month and Unity keeps corrupting my projects. I've tried countless fixes, multiple reinstalls and other ideas I thought might help, all to no avail. But something I've just noticed is that the crash log (Unity opens my project for about 5 seconds then closes it, and opens the bug reporter exe) says:

151215 21:59:17 ------------------------------------------------------------ 151215 21:59:17 Instance starting, version 5.2.0f3_e7947df39b5c, UNITY_WEB_ENABLE_AUTODOWNLOAD: 1, GetDisableAutoUpdates(): 0 151215 21:59:17 Datafile https://gamebucketio.s3.amazonaws.com/GAMES/3e1a5818-6841-497e-ad1f-cc52a3e083b9/Resource+Building.unity3d 151215 21:59:17 Setting error display: 'Failed to download data file', details: 'Download failed, please retry', link: 0

It's trying to download something, but what? And also, look at the version- 5.2.0f3; I have the latest version of unity (5.3.whateveritisnow). Also, che3ck out the manager log:

151215 21:59:17 ------------------------------------------------------------ 151215 21:59:17 Manager starting, version 5.2.0f3_e7947df39b5c

Again, it's starting something for the wrong version of Unity.

Does anyone know what's going on here or how I might be able to fix it? I can't continue with development and I have a whole team of staff waiting on me to sort this out. Please let me know if you have any suggestions or ideas, I'd really appreciate any help I can get!