No worries, sorry for the jargon. NDR stands for Non-Delivery Report.
From your description,
1) You've already changed the password (best to be done using another phone/tablet/mac that is confirmed "clean", not all but most viruses are platform/exploit dependent)
2) Returned mail topic "MY DEAR YOUR COMPENSATION FUNDS PAYMENT ORDER VIA ATM CARD"
3) NDRs continue to flood inbox despite PC being off
4) The timestamp of the NDRs received falls within the duration when your PC is off
If all terminals you use to access corporate mail either at home or office is clean then all the points above suggest that scammers are spoofing your email to send out spams. Your email account is likely to be still safe and uncompromised. For the spamming, there is nothing much you can do though but to besides filtering on your end.
Can also try scanning using MBAM, its free
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