Sine the icon is the generic one, it seems the path may be wrong. right-click on the icon and choose properties and see what directory it points to.
After clicking properties, click the change icon entry and it should bring up Thunderbird and select the first icon in the list, then choose Apply and OK.
Operating System Windows 7 64-nit
Computer Type E-Machines (Customized}
CPU Type and Speed AMD Athlon™ II X2 250u Processor 1.60GHz Max 1.60GHz Ext 200MHz Cores 2 Threads 2
Motherboard Chipset eMachines
System Memory Type 6GB DDR2 RAM DIMM Speed 266MHz
Video Card Type and Speed NVIDIA GeForce 8500 GT 512 MB memory with HDMI out
Computer Monitor Vizio 26" HDMI monitor
Hard Drive Seagate ST375052 8AS (500GB) and WD25 00AAKS-00VSA (250GB)
Optical Drives HL-DT-ST DVDRAM GH41N
Network Adapter NVIDIA nForce 10/100 Mbps Ethernet
Anti-virus Software PC Tools Spyware Doctor with Anti-virus
Computer Skill Level Certified Professional
Windows Experience Index 4.5