As you have just discovered truly faulty SIM cards are very rare, dirty contacts or incorrect seating/positioning are much more likely.
Your Virgin SIM works in ANOther handset. An O2 SIM works in your LG. So likely your Virgin SIM is fine.
Hence I am wondering if the LG is set to 4G/LTE only. Virgin Mobile does not support 4G/LTE modes. Only 2.5G & 3G modes are supported. So look in the settings and see if you need to enable or switch on 3G. Switch off 4G/LTE or 4G/LTE preferred and then power off the handset and then power it on again and see what happens.
For Android Marshmallow this setting is found in Settings>Wireless & networks>More>Mobile networks>Preferred network type