I've browsed the forums over and over and haven't found anything that answers my question, so I hope I'm not being redundant here.

I initially had Minecraft on my Mac, and it works just fine aside from the occaissional lag. I once transferred it to my PC via flash drive, and it worked fine again. It ended up getting deleted from my PC, and by then I'd lost my flash drive, so I borrowed a friend's and put it on there again. Now, no matter what sort of zipping/unzipping/compressing programs I download or what files in the Minecraft folder thing I try to open, the game itself will not run. I've tried deleting it and trying again, to no avail. Changing the file extension to .exe only makes it come up as a bunch of coded text (gibberish to me!).
I know someone will probably answer "Just get it from the Minecraft website again!" I can't really do that, my PC has been having issues with its web browsers as of late. 
Anyone know what to do?
I have an HP with Windows 7, if that info's of any use.