Hate to be the bearer of bad news, but it looks like hardware failure. I have seen this at my work numerous times, where users simply turn on their workstations an are met with this type of error. The fact that the BIOS does not see the hard drives tells me that it is more than simply a Master Boot Record issue. My suggestion is to call DELL if the system is still under warranty and have them replace the hard drive. Or simply buy a new Hard Drive at retail and throw it into your system. Good luck.