Acquired machine last year with many probs. Help from hear and my local electronics whiz tracked down several bad components and we got going with a couple of ultra simple parts(conversational programs). This has been a neglected project which I am now resuming.

Am now trying to program a more elaborate part. I've entered about 35 events. When I power up the machine and go to my program, I am finding unrelated events. I have already deleted old programs and have lots of storage space. When I open my new in-progress program, I attempt to go through event-by-event to review and confirm. I get to maybe the 15th event and a strange one appears,which I delete and/or edit. After a couple of "next event" moves, I lose my screen and get an error message (#100_ disc read error. cut power and repower). I then get back into the program a and it crashes again. The couple of smaller old programs are still OK and you can scroll through all their events_ no prob. For that reason, I hope my hard drive is still OK.
OR IS IT?

Anybody have any ideas? I can't see what I can be doing in the way of entry errors that could create these incidents. I am afraid it is a computer-related problem. (Bad hard drive?)

As always, any suggestions appreciated.
I am told a Centurion VII upgrade would be good but, being totally green in all this, I want to get control of the beast as is before getting involved with another devil I don't know.