Have to agree with the other replies: this could be any number of things. I’d start with the basics by making sure it’s not a hardware issue, then looking at software. Vostro is Dell’s budget business line, and my experiences with Vostro have been lackluster at best.

That’s not to say it’s purely a hardware issue. I’m a hardware guy so I tend to look at hardware first. Any number of software issues could also be causing your issue, including drivers, driver configuration, data corruption on your storage device, a setting or config from your distro or upstream provider, or even some random utility you installed.

Does it crash under other operating systems? Does it crash only after sitting idle for a certain time? Are you able to open another TTY and use the system from a prompt even though your screen is black?