Thank you for marking my answer as a solution and the feedback. I'm glad you got it working again.
I recently had to re-seat my RAM per the error code. When the error code came back later, luckily, a restart took care of it. I realized my RAM is a little dicey and is probably showing its age. It doesn't like too many things open on the taskbar and it doesn't come back from standby/sleep. Depending on how much activity, probably my safest bet is to restart to clear out the RAM before putting back to sleep. - Until if I get new RAM.
I bet your T5500 still whips. Still a smart move getting a newer computer and having the T5500 as a backup.