What Moodle version are you using (always provide this info, along with your server environment: web & database servers used, versions, php, hardware)?
If everything happened after the server issue, did you start by checking that the server is actually without any problems anymore? Check your server (web and database) configuration files and error logs (very important). If you are having corrupt files after uploading them I'd say that this must definitely be a server configuration issue. It could also be that current files in moodledata were damaged after the server issue you mention.
Please enable debugging:
Please run the following SQL statement:
WHERE contenthash = '5235a458c879cdae2f8dcec877a5c6998921843d';
Also go to moodledata/filedir/52/35 and check file 5235a458c879cdae2f8dcec877a5c6998921843d.
Have you checked disk space?
Sometimes, seemingly unrelated things actually create problems; please disable any Moodle plugins you might have installed. Switch to the standard theme. Purge the cache (Site Admin > Development > Purge all caches). It could be a browser issue on your side; an add-on or a plugin could be interfering with the upload. How about virus and/or malware?