We have a 7010 that has odd boot issues. Often you boot, you get the Dell logo, the Win 10 logo flashes up and then it powers down. Then on a second attempt you get Dell logo, Win 10 logo and then the 'spinning ball bearings'. Once you see the ball bearings, you know it's going to start. The start and promptly stop can occur once or half a dozen times, but so far at least, it does eventually sort itself out and start.

So far I have...

1. Removed and re-seated the HDD cables ... but I have NOT looked to swap to a different SATA port (if there is one in a 7010??)
2. Run complete HDD diagnostics and no issues
3. Run Support Assistant and no issues
4. Checked the BIOS level (A29)
5. Checked and reset the BIOS settings
6. Run a BIOS-level hardware test ... and everything passes

On the BIOS side...

1. Legacy boot enabled with HDD as primary boot device
2. Selecting UEFI which I would expect to be an option (Win10, 3 year old box), there are no book options. 'Add Boot Option' comes up with 'File System Not Found!' ... suggesting it can't see the HDD, but see 4. below
3. SATA is set for AHCI
4. Drives shows SATA-0 being the internal HDD so disk is being recognised (SATA-1 is DVD+/-RW)
5. Secure Boot is disabled

Anyone any ideas on this odd 'will start eventually' behaviour, and given all checks pass, quite what can I try to identify and resolve this issue. Kind of concerning to have a machine become so unreliable.

Thanks for any thoughts