This is a pretty well‑known iDRAC7 quirk on R720s after a full AC power loss.

What’s happening is iDRAC boots, but the web service doesn’t come up, so the GUI is dead until you reset iDRAC. Rebooting the server alone won’t fix it. Having another “identical” R720 that works fine is totally normal.

Things that usually help:

• Clear / reset the Lifecycle Controller (F10 at boot)
• Reflash iDRAC firmware without preserving config (even if it’s already latest)
• Drain flea power (pull both PSUs, hold power button ~30s)
• If using shared NIC, try switching iDRAC to dedicated
• Make sure updates were done in order: BIOS → iDRAC → LC

If it still happens after that, it’s usually hardware aging (iDRAC/BMC or motherboard). Fairly common on older R720s. Only real permanent fix then is a board replacement or avoiding full power removal.

 

Hope that helps;!