windows - Downloads are corrupted

Almost every file I download is corrupted. I have to use my second computer on the same network to download my drivers to install.

At first I thought it was my Intel SSD, so I removed it and tried running on my spare harddisk. Didn't help.

Then I tried running memtest86+ v2 and no errors were reported. (I'm downloading Ubuntu now using my second computer to run an updated version of memtest)

I've ran chkdsk /F on the harddisk and no errors were found.
On my SSD, I did a secure wipe and some tests using Intel's SSD tools and no errors were found.

My Chrome browser keeps crashing, so I thought it could be my graphics card since Chrome uses hardware acceleration right? So I bought a new graphics card and still there are errors.

I manged to get my MMO installed and I don't seem to have any problems running it.

So my final guess is either my CPU or motherboard is dying.

Are there any other tests I can do to find out the problem?

Update:
The computer with the problem is connected to my router using an ethernet cable, I just changed this cable a few months ago.

I shared the folder with the downloaded drivers on my second computer using Windows 7's homegroup, and installed it from there so I think the network is working fine.

Update 2:
When I downloaded my graphics drivers and tried to install them, it says something about the file being corrupted, and I need to download again. It happened for my graphics drivers, a game patch, chrome installation file, and maybe the windows update files because I got a blue screen during the windows update. Something about the ntfs.sys file.

When I reboot, I couldn't boot into the OS because of a BSOD with the error "Page fault in non paged area". I had to go into repair mode and do a system restore before everything went back to normal.

Update 3:
I ran Memtest86+ v4.2 for 8 hours, 4 passes, 0 errors.

Update 4:
I ran OCCT, CPU:OCCT test and it reported an "error on Core #3". I disabled it in BIOS and ran the test again, this time it just says "error detected". I suppose my CPU's causing the corruption problems.

Answer

The problem was found to be the CPU or maybe the motherboard, as I don't have a spare motherboard to test. Thanks for all the help!