Hello and welcome to Tom's Hardware Forums.
Restart it and tap whatever key the first screen tells you that you need to go into BIOS or Setup - Delete or Function 2 are regulars. One in, seek out the setting to restore Optimal Defaults or similar, accept that one, save the changes and see if the message disappears.
I've worked on a number of Toshibas where this has happened and BIOS is password protected - often where it never previously had been - and I've yet to find a way round that so hopefully, that isn't your problem. If it is, however, your data can still be retrieved by taking the hard disk out.