gateway dissappears everytime i restart my system....

I'm seeing more of this issue and have experienced similar problems. I'm not sure yet of THE solution, but there are things you can try.

1. Check your router log for any attacks. Most routers can fend them off. My neighbor downloads stuff from torrent sites and he has lots of Denial of Service (DoS) attacks as well as a few other types.
   
   What can you do if the log contains lots of attack entries?
   Suggestion 2 advises you to power down your "cable modem". This might give you a new IP address from your ISP - although it might not.
   
   You could ask your ISP about the situation and see if they will reprovision your device.
   
   If you visit sites that are known to initiate attacks (many peer-peer and torrent sites), you should stop going to the sites.
   
2. Try to sync the "cable modem" and router. If you have access to the devices, power off the router, then power off the "cable modem". Wait for a few minutes, then power on the "cable modem"
   DO NOT power up the router yet. The "cable modem" has to uplink with the server. Lights on the device will flash and then go steady. Once the device is all steady on, then power up your router. Wait a few more minutes and try to connect.

Information on the IP address you're receiving:

iana.org said:

Special-Use Addresses
Several address ranges are reserved for "Special Use". These addresses all have restrictions of some sort placed on their use, and in general should not appear in normal use on the public Internet. The overview below briefly explains the purpose of these addresses – in general they are used in specialized technical contexts. They are described in more detail in RFC 5735.

"Private Use" IP addresses:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

These address blocks are reserved for use on private networks, and should never appear in the public Internet. There are millions of private networks (for example home firewalls often use them). People can use these address blocks without informing us, so we have no record of who uses which of these addresses.

The point of private address space is to allow many organizations in different places to use the same addresses, and as long as these disconnected or self-contained islands of IP-speaking computers (private networks) are not connected, there is no problem. If you see an apparent attack, or spam, coming from one of these address ranges, then either it is coming from your local environment, your ISP, or the address has been "spoofed".

The Private addresses are documented in RFC 1918. If you have further questions about RFC 1918 usage, please contact your ISP.

"Autoconfiguration" IP Addresses: Addresses in the range 169.254.0.0 to 169.254.255.255 are used automatically by most network devices when they are configured to use IP, do not have a static IP Address assigned and are unable to obtain an IP address using DHCP.

This traffic is intended to be confined to the local network, so the administrator of the local network should look for misconfigured hosts. Some ISPs inadvertently also permit this traffic, so you may also want to contact your ISP. This is documented in RFC 5735[/URL].

If resyncing the devices doesn't help, try hardcoding the IP information as an alternate configuration.
You haven't provide much detail about your network configuration, so I'll use my network as an example.

Network & Sharing - Manage Network Adapters,
Rt click your wireless adapter and select properties
select IPv4 and click the properties button

On the General tab:
Obtain IP address automatically
Obtain DNS automatically

On the Alternate Configuration tab:
Hardcode addresses for your network, my router is configured for a 192.168.1.1 gateway / DNS server

The last number of the IP address is up to you - as long as other devices aren't assigned the same number.

I plugged in the Google DNS servers just to see if the gateway DNS function was at fault.

IP address: 192.168.1.42
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.1.1

Preferred DNS Server: 8.8.8.8
Alternate DNS Server: 8.8.4.4

This works for me, but it seems as though there is an underlying issue. It's slow to connect, but ok once connected. Sometimes I get an IP address from the router, other times I get my hardcoded IP address.

Hope this helps your situation.