Windows 7 Network Issues

I am hoping someone could at least give me some suggestion as a possible cause to my network issue and/or solution. First my setup is this:
- DLink Network Router (DIR655)
- I have a custom built PC (Asus P8Z68-V Motherboard Gen 3) with Win 7 64 Bit SP1 (latest updates applied), i7 CPU, 16 GB RAM
- iMac 2007 (no network issues, full speed connectivity)

Issue
- After playing an steam based game, I was noticing some system lag, and thought I should reboot since I hadn't restarted in a few weeks
- Following the reboot the network icone on the taskbar with the exclaimation point
- I reboot again nothing changed
- Tried different ports on the router, no change
- The indicator lights on the On Board Ethernet port on the motherboard shows solid green for the speed indicator, and blinking orange on the Activity LED.
- I checked the cord, no difference
- No issues seen with iMac
- I checked my Router Network status and the PC MAC address is listed with an assigned IP, but I am still unable to access Steam or the Internet, and the exclaimation point on the network indicator is still present.

Options to resolve that I came up with:
1. Purchase a add-in network card and see what the result
2. Purchase a new router (I think this is the last resort)
3. Use a another hard drive to re-install windows on and see if the network (on-board) still functions


Any thoughts or recommendations?

Have you restarted the router/modem?

What is the message that it gives you? An exclamation point could mean a lot of different things.

Sorry, good points. I have restarted the router, and the exclaimation states "no network connection"

In the network devices list, does it show it is disconnected? What is the status of the device?

Yes, it does. Even though the MAC Address and IP has been assigned and the PC name is visible in the router network item list.

I recently had to set a NIC card's network speeds (10/100/1000) manually in device manager options to get it to work (in my case had to set it to gigabit or it would only connect at 10Mbps for whatever reason).

Sometimes simply reseating the network cable in the NIC will help.

Unplugging all power to the computer for 10-20 seconds is worth the minimal effort too.

Definitely a strange issue.

I will give the manual setting a try, and I have tried the power off, unplug and event change network cables.

I left the system powered off all night and on boot up this morning the same result...

Tried removing the NIC from Device Manager, reinstalled with fresh drivers. No success. Trying a system restore point from 2 days ago, and that worked. Very strange ... even more so because windows 7 states the restore failed....

Thanks for all you help and suggestions, guess the restore point should have been my first try.