NSIS Error from downloading Unity

I'm trying to install Unity on my computer. However, during the download/installation, it keeps failing its self-check. It gets to 100%, but then it shows that it has encountered an NSIS error. It gives me three options: Abort (which cancels everything), Retry (which doesn't give me any better results), and Ignore (which "completes" the download, but I can't find any executable files in the destination folder). I've tried a lot of things, but nothing seems to be working. As a last resort I could try bypassing the check, but I'd rather not do that if it might be a server-side error or if there are any routes I have not yet tried.

I've uninstalled and tried to reinstall it, several times.
I've cleared the cache.
I've restarted the computer.
I renamed the installer.
I don't have any download accelerator/manager programs.
I ran a virus and malware check.
I tried it after disabling my anti-virus.
I tried it after disabling my firewall.
My hard drive is showing no errors.
My drivers are up to date.

My setup:
Dell Vostro 230
Intel Core 2 Duo CPU, E7500 @ 2.94 GHz
3 GB RAM
Windows 7 Home Premium
Inherited from my grandparents, so it's practically factory-new

 

Have you tried using the full setup download, instead of the installer? You can get to those on the download page under "Additional Downloads"

 

I tried it, but it skipped straight to the self-check and failed again.

 

Really sounds like you have a virus infection.

 

I've already done virus sweeps.

 

Just to cover all bases, you're not using Norton Antivirus are you?