Firefox will not load and cannot download anything with

Just upgraded to 7 from Vista.

Since the upgrade Firefox will not load. No error messages, just nothing when double-clicking the icon.

I thought I would try and download a new version of Firefox, however tuirns out that every time I try and download anything using IE8 it stops working.

The details of the IE8 error are:
Problem signature:
Problem Event Name: APPCRASH
Application Name: iexplore.exe
Application Version: 8.0.7600.16385
Application Timestamp: 4a5bc69e
Fault Module Name: StackHash_0e76
Fault Module Version: 6.1.7600.16385
Fault Module Timestamp: 4a5bdadb
Exception Code: c0000374
Exception Offset: 000c283b
OS Version: 6.1.7600.2.0.0.768.3
Locale ID: 2057
Additional Information 1: 0e76
Additional Information 2: 0e765f55dc2578acbcf3f43566e3d33a
Additional Information 3: 2e1c
Additional Information 4: 2e1c341a230656a0ec3a6e6c59de1212

Can use IE 8 for anything else (so far!)

Hi thanks for the prompt response - tried repair but still having exactly the same problem. Had uninstalled firefox but when tried to download using IE8 I still get the same problem as in IE8 stops working.