I was infected by a Trojan it's synced in Dropbox, too. What should I do?

I should add that when I try to reinstall DropBox I get that error, followed shortly by a popup box reporting Error 2. It doesn't install.

I believe this may have something to do with Dropbox per se, as it doesn't appear to just be limited to users of Iolo System Mechanic.
This is my experience regarding this issue, in case it helps someone, which I have just discovered has resolved itself.

Timeline:

Tuesday, 03/20/2018 afternoon - Iolo System Mechanic System Shield Pop-up window appears stating it found a file infected with the Eldorado virus, said file at this initial report was:

[ALL CAPS] - c:\program files (x86)\dropbox\client_46.3.60\psutil_psutil_windows.pyd
is infected with w32/s-462f1630!Eldorado, and System Mechanic quarantined the file.

I know that there should not be, other than during upgrade installation, other 'client' folders in the dropbox folder.
Next I went to the dropbox folder and visually verified that there actually was both a 'client' folder, and a 'client_46.3.60' folder created on this same day. There are indeed both.
At this point I assumed an automatic background upgrade installation had been in progress (I've had DropBox on this laptop for 7+ years).
I then ran a full system malware scan, and, in addition to that file, it found and quarantined a total of three more files, all infected with the same version of Eldorado, as follows [paths ALL CAPS]:
c:\program files (x86)\dropbox\update\download\{CC46080E-4C33-4981-859A-BBA2F780F31E}\46.3.59\DROPBOXCLIENT_46.3.59.EXE
c:\program files (x86)\dropbox\install\{229A986C-0B31-4104-AB08-95B1F788D7B0}\DROPBOXCLIENT_46.3.60.EXE
c:\program files (x86)\dropbox\update\download\{CC46080E-4C33-4981-859A-BBA2F780F31E}\46.3.59\DROPBOXCLIENT_46.3.60.EXE

Regarding this issue: I did nothing more, other than no longer use Dropbox, for the remainder of this day.

Wednesday, 03/21/2018 morning - I noticed when downloading a Google document I had completed, to a dropbox sub-folder on my laptop for backup and syncing with cloud storage, that syncing was not happening. I checked and discovered that Dropbox had not loaded.

Regarding this issue: I did nothing more, other than no longer use Dropbox, for the remainder of this day.

Thursday, 03/22/2018 evening, just prior to writing this up - I decided to attempt a re-install.

I go to Settings->Apps & features (Win10), click on Dropbox and notice that it's version is 46.3.60 AND dated today, 03/22/2018. I find this very interesting, so...

I performed a 'Google' search on 'Dropbox Eldorado Virus' and found this report I am replying to.
I checked the dropbox folder and discovered the following: The 'client_46.3.60' folder had been removed and the 'client' folder had Date Modified set now to 03/22/2018.
I checked to see if Dropbox was running in the background: It was not.
I found and manually launched Dropbox and the following happened: It succesfully loaded and synced my laptop's Dropbox folder with cloud storage.

Based on this result it appears that by my doing NOTHING since the initial issue began on Tuesday, for me, that this issue was resolved through one of the following:
    Self-correction...
    Dropbox became aware of the issue and fixed it ASAP, ergo the apparent background update installation that happened on my laptop today.
    My leaving the 4 affected files quarantined and doing nothing prompted Dropbox to attempt another background update installation and succeeded.
    Or...

I have now permanently deleted the 4 quarantined files.

Next I will see what happens Friday morning, 03/23/2018, after I fire my laptop back up, and find out if Dropbox starts up as usual or if I have to manually start it, and, if that Eldorado virus returns, which I suspect will not be the case. I'll try to remember to update this report with what I experience at that time.

Dropbox is not a virus.