If some sessions open, consider the following:
1-hold SHIFT while opening a session(which makes all plugins inactive). If this works, then you have a bad/corrupted plugin.
2-create a new blank session and then use the Import Session Data command and import from the troubled session(s). Don't do all the tracks in one shot. Import sections like all drums, then bass and guitars, then keys and vocals. Doing this might reveal a particular track that is causing the issue.
3-if you get any error message, save a screen shot and post it here so others can see the message.
4-Maybe the session is corrupt. While this is a "Hail Mary", it has worked a few times for me; Create a new blank session and change the sample rate(so if the original is 44.1K, make the new one at 48K, or vice versa). Then use Import Session Data and tell the ISD settings to use SRC(Sample Rate Conversion). The change in sample rate causes all the audio files to be re-written, which just might iron out whatever corruption has happened.
5-troubleshooting is an acquired skill. Be methodical(IOW, don't try 10 things at once) and keep track of the steps you try. And, don't forget the backups(assuming you have auto-backup enabled). Fingers crossed for you
