PC cant connect to iPhone over wifi

I'm trying to use an app that transfers files to the iphone via Wifi.

Access is by entering the iphone's IP address and port into a web browser.

I've seen quite a few apps that use this method, so it seems pretty standard.

I've also used this method myself quite a while ago, but now can't seem to get it working.

When I enter the iphone's IP address into the web browser, it just times out.

Tried pinging the IP address from MSDOS from PC and get "Destination host unreachable."

Packets sent = 4, received = 4, lost = 0 (0% loss)

PC can't connect to iphone at all.

iphone is connected to Wifi okay and can access internet with no problems.

Both PC and iphone are on same domain and subnet, ie. both 192.168.1.XX and 255.255.255.0.

Tried disabling all firewalls and AV programs, but that didn't help.

Router sees connection of both PC and iphone with no problems.

So both PC and iphone are on the same network and can connect to internet fine but can't connect to each other.

iphone model is a 3G running OS 4.2.1, which is the latest version that my phone can use.

Can anyone help so I can resolve this issue?

Thx