My Wi-Fi and wireless signal is perfect unless the computer is on?

If my computer is turned off, my iPhone, iPod, PS3 etc. All have perfect connection to the Wi-Fi. The PS3 shows 100% signal strength and everything runs perfectly. The problem is, as soon as the computer is turned on, the Wi-Fi for the PS3, iPhone etc. All goes out completely and our Wi-Fi doesn't even show up as a selectable option. Does anybody know why this happens?

All electronic devices create an EM field. It appears yours is positioned just so as to block the signal to your router. It may also be that your computer is making noise on the electrical line that is causing problems. Be sure you are using a quality surge suppressor with noise filtering, which prevents noise from the attached devices getting to the power lines which can then be repeated throughout the house.

Most Wi-Fi operates in the 2.4 gHz band which is also used by a host of other devices: cordless mouse and keyboard, bluetooth devices, wireless speaker systems, baby monitors, most cordless phones, and microwave ovens only begin the list. In your case, does your computer have any other wireless devices? Blutooth, mouse, keyboard, etc? Try disconnecting those and powering on to see if the problem goes away.

Ask again: (with more details)
I've never heard of this.
Is the computer hooked up with ethernet cable or wi-fi?
I agree the computer and/or cables may be too close to the wi-fi antenna.
Make model of the router?
Are the security settings in the computer unusual?

Try
Disable wireless on the computer in Network connections.
Hook up an ethernet sable to the computer and reboot it.
See if it still happens.
Shut down all devices and remove power from the router for 1 minute.
Power the router and wait 1 minute before powering everything else and test it again.

Run a virus scan and malware scan on the computer.
Like with, AVG and Malwarebytes

Could be many things, but at least you have identified the source of the problem. Get your router and move it far away from your computer and higher in the room.

You need to update the speed for it, call your internet provider and ask them if they can update it may cost a lil bit more but that is the only way you can have the computer, PS3, Iphone etc. To be on at the same time with no problem.

Maybe it's caused by interference. When you have to turn on the computer, you can turn it into hotspot with My Wi-Fi Router, it's software which based on the wireless network adpater and will configure a virutal router.Thus all of the other devices can connect to Wi-Fi connection at the same time.