Business Computer locks up after hour or two of use

Hello sevenforums; I work for a small american auto restoration parts company, and I am troubleshooting a problem with our computers. One of the computers (there are 4 networked through LAN) continuously locks up after being on for a while. Recently our computer tech guy who supposedly is a professional business network support person installed DropBox and I was wondering if that is what is causing the problem because it has to continuously port all activity through another internet software platform. Regardless, 9/10 times it now just locks up and won't load and we would just have to shut it off and start it back up. I am weary that this is a virus program, but using Malwarebytes has not helped the situation in any way.

Should I try to restart in developer mode and run some anti virus software? Basically my last ditch effort was to suggest that we just buy a separate harddrive, save all of the document-style data onto it, swithc to developer mode, run a virus scan then completely wipe the hard drive after defragmenting and re install windows 7. If worse comes to worse, would this fix the problem? or does my solution overlook some means that malware and viruses can stay hidden in hardware despite my efforts. Any help would be greatly appreciated, since this has basically frozen the productivity of 1 of our 3 computers and employees.

Thanks Guys.

You can configure DropBox to not run at startup and only start it if you ever need to sync with your cloud storage.

Otherwise you can also try a clean startup - Troubleshoot Application Conflicts by Performing a Clean Startup

The computer is 6 years old, it's from 2015 but it is constantly on and doesn't get turned off. Malwarebytes and CCleaner did nothing malwarebytes didn't even find anything. I will try adwcleaner though. But I just bought an external hard drive in order to save all of the business data onto it and then wipe the computer and reinstall windows.

I really need to know what is the sure-fire way to completely wipe the hard drive and other hardware in order to be sure that the computer with it's reinstalled operating system doesn't fall right back into the same problems.

Thanks for all of the replies guys

That's what I'm saying, I understand what Restore Point is but I can't do that because I don't know at what point the problems started, it's not the computer I use on a typical basis which is why I don't have as much information as I would like to have.

Full restore is what I'm gonna do just to be sure about where to go next; nothing of value will be lost I saved all the data to an external and if anything I will just have a clean disk to start over with without any time caused operating system hang ups.

I wouldn't expect that it has to do with poor ventilation because the computer doesn't ever feel heated or anything and it's not clogged with dust or anything