Call the mfg. Period. They will tell you which key to press to access the partition you need to in order to "restore" your Windows O/S.
This is a feature the hardware mfg have come up with to save money on the cost of providing restore discs.
Frankly this sucks because you will have to remove all the trialware they include(and Dell is notorious for this), reinstall any sofware you've added and you will have to install all Windows updates that have been released since you purchased your PC.
regards,
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