Dell XPS 8300

Greetings and Happy Thanksgiving!

In Dec 2012, I purchased a desktop PC (Dell XPS 8300) for my children to use for homework and gaming. Well, you can imagine where the majority of use went on this PC!! I can't prove it, but I'm convinced that all the gaming downloads and server hostings has caused this computer to crash. Now, when I boot her up, I get past the initial POST screen (Dell screen and task bar travels completely from left to right), only to switch to a black screen with a simple one line white text that states, "OPERATING SYSTEM MISSING_" the prompt at the end is flashing kind of like a DOS prompt...

I have tried F12 and F2 to run dell diagnostics and all hardware comes up normal. I've run the memory and THOROUGH memory tests and no problems there either. I have searched through the boot up options and can't seem to find any fixes.

I talked to a Dell support technician and he wanted to charge me $260 for one year technical support and he wanted to send me the original Windows Boot discs. I forgot to mention that I cannot find the original portfolio for this computer and I do not have the original boot software - we moved recently and I think it was lost in the shuffle...

Can you please recommend a course of action? If you think I should take it to a local PC doctor, what would be a fair price to pay for resolution? I heard others on this forum say that the guys at Best Buy would just tell me to ship it back to Dell...I hope that isn't the case!

Any suggestions would be much appreciated and I thank you for your assistance.

Sincerely,
Alex