I have a Dell-Precision 5510 laptop with Ubuntu 14.04 installed. I left it unused for about a month, and when I tried to turn it on, turn-on button lighted up, stayed this way in about 20 or 30 seconds, and then died.  After a few hours, the screen at last lighten up, and after showing the Dell logo, it told me : No Boot Device is found. Press any key to rebooot the machine.   I did it, but it went through the same routine back to the same message. I am terrified; any idea what can be done?
No Boot Device is found
boot;laptop
When my comp got to No Boot Device is found. Press any key to reboot the machine, I tapped the key F2 many times until it open up a page that had a list of various options, and in the top section General I clicked at Boot options (or something like that). It opened another page, which among other things asked me about which option I want to choose -- just two of them -- Legacy and  UEFI; it showed that the current one is Legacy. Following a hint offered by @oldfred (see in Comments)  who mentioned  the term UEFI (beats me if I know what is that:), I decided to click at it instead of Legacy, and it worked! When I returned to a previous page (by clicking Exit), it showed me a starting Ubuntu page! The comp is still telling me that there is an error in system programming, but otherwise I am happy to have at least my data back....