I would advise strongly against altering anything on the HD, until you have explored the possibilities of looking at the OS again.
If it helps:
Partition 2 would be the a Fat32 partition, installed by Dell. It contains the utilities which to run the dell Diagnostic facility.
Partition 3 Is the normal (of latter days!) Boot partition, installed automatically, at the same time as the OS.
Patition 4 is the Intel hardware recovery. This is something nearly always put in by dell. Its purpose is to make sure your hardware is kept up to date. It is a waste of space and is linked to software on the OS, concerning Intel management.
Partition 5 is a spare data partition, with or without data. depending on the previous users preference, it could contain a complete OS
Partition 6 is the Microsoft backup partiton.
Have you tried altering the bios settings in the boot section, and selecting Legacy mode, instead of UEFI? At the same time experiment with secure boot off - you can always reinstate it later.
Entering the bios, varies from one dell to another. Normally I thrask both F11 and F12 immediately on start up, and wait for the option menu. Another choice may be to wait for the Dell logo an then hit F2,
Whilst in the bios. Make sure that the first boot order is, indeed the correct HD or path.
Bi locker would only be on the pro release. An OEM is normally the basic OS, but, in the case of Dell, can be a pro, according to the cost of the machine or customer request. You could check this, possibly, by running WinVer from the command prompt. I have never tried it from an initial boot, but it may be possible.