clicking on .crdownload file crashes explorer.exe

Reinstalled Win 7 Ultimate 64 on an SSD two days ago, and immediately installed Chrome. Twice since then, chrome had a download crash at 100% and was unable to download new files, and when I looked in the download folder there's a crashed download (eg: Unconfirmed 508279.crdownload).

The trouble is, I can't click on it. If I left click, right click or interact with it in any way (including select-all in the folder and shift-delete) explorer.exe immediately stops responding and has to be restarted. I haven't found anything via google about explorer.exe crashing when you click on a file.

In safe mode, I can click and remove it without issue, so I'm assuming it's something I've installed that has hooks into explorer, but the first instance of this happened when I was very early in the application-reinstall process. Avast, 7zip, WinRar, Dropbox and Google Drive are the primary culprits based on timing. There are other possible applications like office, and a help authoring toolsuite I use, but to my knowledge they don't hook into explorer at all, so I don't see how they could be an issue when they're not even running at the time.

Everything that is currently installed on the PC was previously installed on the same PC without this issue (same everything: the only difference is it now has more RAM and an SSD).

My powers of deduction kinda end here. Is there an easier way to identify the culprit than uninstalling things bit-by-bit and waiting to see if it strikes again? This is a business PC, and I use those programs, and I can't reliably reproduce whatever is causing Chrome to spit the dummy on that download for testing. I'm hoping there's a log file or something I can look at that will help narrow it down. Thanks in advance.

I thought I had, because I ran through a bunch of updates, and I believed Windows Update when it said there weren't any more updates, but I just went to check again, and SP1 isn't installed. I've tried the past 36 hours to get it to install and it won't, so when I fix THAT problem, I'll report back about whether that fixed this problem.

Are you trying to install Enterprise or Ultimate?
Which one do you have the proper COA key for?

The install disc had both "Ultimate" and "Enterprise" printed on the label--I thought "Enterprise" referred to the fact that it's a volume license (registered via MAK key), and "Ultimate" is the edition that is installed, so I listed both. It says "Enterprise" under Control Panel > System. (Sorry for any confusion, please correct me if I'm wrong.)

How are you installing it? You can download it here:

I have tried Windows Update, and downloading the update to install manually, both in normal operating conditions, and then stopping all unnecessary services and unplugging the network cable--that resulted in a BSOD halfway through (0x0000007a / 0xC0000185 relating to ataport.SYS, but I haven't replicated that). Usually it just gets stuck with the install bar halfway through. I left it go all night, it was still the same in the morning. When I tried again this morning, it seemed to skip right to that middle bit and get stuck again, so it seems like it's not rolling it back fully, maybe?

For completeness sake: I was not able to get SP1 installed, there turned out to be something very very wrong with my installation (thread here). I did a full format-reinstall with an SP1 ISO, and so far the problem has not recurred.