Hi [NAME], Mentioned was 2 different sets of RAM.  One thing to try is just the exact matching pairs.  If not in slots 1 & 2, then 1 & 3, etc. However, I mainly think the PSU is toast.  Especially if you can't even access F2 BIOS or the F12 Boot Menu and the thing dies. Too many error codes were thrown for that part to be useful.  It's useful if it stops at 1 error code.  Mazzinia was right with the new battery attempt as confusing error codes, and other issues, are sometimes thrown with bad batteries.
I have a problem I'm struggling to solve and would really appreciate a pointer or two! The PC boots to windows, asks me if I want to repair start up and then the power cuts out. The error light configuration: At power on 3 and 4 flash three times and then they are solid with a hard drive symbol? above. A few seconds later I see 1 2 and a flashing HD symbol 1 2 3 and a solid HD symbol Finally solid HD symbol  no numbers The power off then happens.   I have six 8 gig ram sticks. I removed the ram from 3,4,5 and then exchanged it with 1,2,3 (in banks 1-3) so testing several configurations of ram. I'm lost now. Thank you!!
T5500 not booting. Powers itself off