There is a problem with your JIRA access.

[nicolaspansardi]

My Jira instance is hosted in a VM, which had stopped this weekend.

This Monday when I tried restarting I've got "JIRA access problem" on my browser with the following description: "Unexpected exception during JIRA startup. This JIRA instance will not be able to recover. Please check the logs for details".

I tried reading my logs but I don't have a clue how to solve that. My last backup is outdated so I wouldn't want to uninstall everything.

In one of the logs there is a "SQLException: Cannot create PoolableConnectionFactory" so maybe it is something with the native Jira DBMS. 

Please help me.

[Nic Brough -Adaptavist-]

The SQL exception is the main culprit.  It means Jira can't connect to the database, so there's no chance of it starting up.

It worries me that you say the "native Jira DBMS" - there is no native one, but I guess you mean the embedded one (it's an off-the-shelf file and memory based, called H2).  This is scary because it can fail catastrophically, and your SQL exception could be a symptom of you having lost it.  You might want to check for backups...

Have a look at the logs in more detail, they should tell you if that has happened.