820-00281: Fan spins and CPU warm but no usb activity

Have this board that doesn't boot. The fan spins and the cpu is warm but no usb activity. First i found previous work done, they had soldered C4109 to R4457(1) and to ground. This is due to it's pads being missing. In anywise, i corrected the cap connection by soldering it to C4110 (1) and ground. I do get .6v for PP0V6_SLEEP1_BUCK0. I currently don't have an identical board, but a 00239 also reads 0.6v too.

The below reading from U7800
PM_PCH_SYS_PWROK - 3.3
PM_PCH_PWROK - 3.3
ALL_SYS_PWRGD - 3.3
PM_RSMRST_L - 3.3

Granted, it appears U7800 does have sign of corrosion clean up.

Do you get VCORE and PLT_RST_L?

PLT_RST_L are reading - 3.3
CPU_PWRGD - 1

PPVCC_S0_CPU - 0.7
PPVCORE_S0_GPU - 0.9
GPUVCORE_PGOOD - 3.3
GPUVCORE_EN - 3.3

PPVCCIO_S0_CPU - 0.98
PPVCCGT_S0_CPU - 0
PPVCCSA_S0_CPU - 0.9
PP1V2_S3_CPUDDR - 1.2

Try known good BIOS...

Would you happen to a good BIOS or is a clean ME enough, which i already flashed with the same result.

When board doesn't boot, if you suspect BIOS, need to try FULL known good working BIOS.
Clean ME region on it, of course.

Put in good BIOS and clean ME. Same issue.

"PPVCC_S0_CPU - 0.7"
Board starts with this value, or do you note some variations in the first 10s?

Did you check each time for USB activity?

PPVCC_S0_CPU starts at around 1.09 and then regulates until it stops at 0.7
When i plug in my usb adapter, it flashes on for like a second.

Not easy to work after someone else.
Inspect for other knocked off components.