I have installed salesforce cli windows 64 bit and I also installed it through npm globally. 
I am on windows 7 machine and behind a company firewall and I have proxy set on my computer

C:\Users\XXXXX>sfdx update
panic: Get https://developer.salesforce.com/media/salesforce-cli/sfdx-cli/channe
ls/stable/windows-x64: dial tcp XX.XX.XX.XX:443: connectex: A connection att
empt failed because the connected party did not properly respond after a period
of time, or established connection failed because connected host has failed to r
espond.

goroutine 1 [running]:
panic(0x6632a0, 0xc0420067b0)
        /usr/local/go/src/runtime/panic.go:500 +0x1af
main.must(0x7b92c0, 0xc0420067b0)
        /home/ubuntu/.go_workspace/src/github.com/heroku/cli/io.go:115 +0x63
main.GetUpdateManifest(0x6a4875, 0x7, 0x6a3c0d, 0x3, 0x7b92c0)
        /home/ubuntu/.go_workspace/src/github.com/heroku/cli/install.go:104 +0x2
72
main.GetUpdateManifest(0x6a4875, 0x7, 0x6a3c0d, 0x3, 0x0)
        /home/ubuntu/.go_workspace/src/github.com/heroku/cli/install.go:102 +0x2
f4
main.Install()
        /home/ubuntu/.go_workspace/src/github.com/heroku/cli/install.go:33 +0x10
0
main.main()
        /home/ubuntu/.go_workspace/src/github.com/heroku/cli/main.go:18 +0x3a