Hey, guys, I bought my PC two years ago (aiming for mid-end):

The applications that are usually on are: Vivaldi/Firefox, iTunes and Tally in foreground and Steam and qBittorent in the background while stuff gets downloaded. For the first 1.5 years, my computer could manage the load without significant lag but for the past three months, it is terribly. Atrociously. It barely manages to open Firefox. Can't multitask. Takes several seconds just to open Task Manager (computer hung when I tried while writing this.)
I have an annual contract with a computer engineer who says that our computer can't handle so many processes which sounds like baloney because what's the point of a mid-end rig if it can't handle Firefox/Tally/qBittorent? (The applications mentioned earlier are max scenario; the current three being more likely).
I erroneously downloaded a Windows crack today which I thought to be genuine. The read-me file had 'lololol'. I did a malware scan which came clean and a virus scan which showed 7-9 suspicious files (I use eScan). The antivirus didn't delete the files so I deleted them manually through Everything.
With just Firefox and Steam open 89% of the memory is consumed.

What can the problem be?

The applications that are usually on are: Vivaldi/Firefox, iTunes and Tally in foreground and Steam and qBittorent in the background while stuff gets downloaded. For the first 1.5 years, my computer could manage the load without significant lag but for the past three months, it is terribly. Atrociously. It barely manages to open Firefox. Can't multitask. Takes several seconds just to open Task Manager (computer hung when I tried while writing this.)
I have an annual contract with a computer engineer who says that our computer can't handle so many processes which sounds like baloney because what's the point of a mid-end rig if it can't handle Firefox/Tally/qBittorent? (The applications mentioned earlier are max scenario; the current three being more likely).
I erroneously downloaded a Windows crack today which I thought to be genuine. The read-me file had 'lololol'. I did a malware scan which came clean and a virus scan which showed 7-9 suspicious files (I use eScan). The antivirus didn't delete the files so I deleted them manually through Everything.
With just Firefox and Steam open 89% of the memory is consumed.

What can the problem be?