Could be anything. First you have to find out if:

1.The Router is disconnecting from Talktalk internet.

2.Your laptop/pc wireless is disconnecting from Router.

3.The strength of the wireless signal from the router to your laptop/pc (should be 54Mbps

4.If it still happens if you connect to the router with an ethernet cable.

Do you have ADSL or FTTC (fibre). If you have ADSL have you got the filters plugged in for all the phones etc, as if not that causes the router to constantly disconnect and reconnect to internet. Have you tried plugging the router into the connection behind the master socket's faceplate? (that cuts out all the phone extensions and if you still get disconnections then you can be sure it is not your internal phone wiring)

Virus or malware.... unlikely but hopefully you have done full scans with your antivirus and an anti malware program malwarebytes is recommended and is free. Malwarebytes Anti-Malware Free (don't be tempted to get the paid for Pro version, the free one is what you need so you can just run a scan when you want to)

As for restoring back to factory settings on the Compaq cq60, that will depend on the Op Sys you have (XP, Vista, W7) and if that is the original Op Sys you had.