If Thunderbird will only run in Windows safe Mode then another program on your computer is interferring.

First check your Anti-Virus/Firewall software. It may need to be reset to 'Allow' Thunderbird.

Toad-Hall said

If Thunderbird will only run in Windows safe Mode then another program on your computer is interferring. First check your Anti-Virus/Firewall software. It may need to be reset to 'Allow' Thunderbird.

Thanks Toad-Hall. I run AVGs Firewall. I checked the settings and noted Thunderbird was in the "Allow" list. Nevertheless I disabled the firewall temporarily but still Thunderbird did not start. I then checked Windows Control Panel Programs and listed programs by date. The only program listed as installed near the date the problem first manifdested was Thunderbird itself. decided to uninstall Thunderbird, download new version and install. Alas this also refuses to start.

Just had a thought, do you only have one instance, the current version of Thunderbird in your Control Panel > Program and Features? Make sure there is only the current version.

On one occassion I had Norton set to allow, but it seemed to be allowing the version prior to an update. So I had to reallow it by unsetting and resetting after making sure I only had one installation of TB.

Then check to see if there is a virus or malware that is causing the issue. download malwarebytes - there is a free version.

• https://www.malwarebytes.org/lp/lp4/02_r/?gclid=COfA_Zi39cICFYLnwgodioIA9A

Start computer in SAfe mode and then run AVG Anti-virus. then run malwarebytes.

Restart computer as normal. Test to see if Thunderbird will run.

Thanks Toad Hall. I have had the free version of malwarebytes installed for some time. however I have never run it in Safe Mode. I followed your advice re running both malwarebytes and AVG in Safe Mode - but no improvement. I have also disabled all Thunderbird add-ons and plug-ins - but no improvement!!

What happens if you right click on Thunderbird icon and select 'Run as Administrator' ?

Running the scans proves that you do not have a virus etc. Running TB in Windows Safe mode proves TB is ok, but another program is stopping it. It also means you can eliminate the Windows default settings and basic device drivers as possible causes.

Suggest you test to see if startup items are casuing an issue. So, try disabling your startup programs. Start > Run > type: msconfig and click on OK (Note: Run may be located Start > Programs> Accessories > Run)

click on the 'Startup' tab

This part is rather boring as you need to disable startup programs and restart computer to take effect then test to see if TB starts ok. When TB starts ok, you will have identified which program(s) caused the issue. Start by disabling the last items in the list, suggest you do about six items. Then if it runs you know the problem lies with one of those six disabled items.

Thanks Toad Hall - apologise for late response. I tried running from Admin - didn't work. I tried disabling start-up programs using technique you proposed. I found 21 lines in the file and disabled 6 at a time but still Thunderbird didn't start. The only line I have not yet disabled is Microsoft Windows\ehome and I was not sure if that could be disabled.

Meanwhile - and hence the delay in my response - I took my tower to a local IT expert. He could find no explanation other than finding some bad sectors on the hard drive - which I can't find using CHKDSK.

Not wanting to give up I checked the Thunderbird program file on my Netbook (which this msge comes from) and my desktop. I found the following three files on the Netbook missing on the desktop (Vista):-

icudt52.dll icuin52.dll icuuc52.dll

Could this be the problem or is it simply that the Netbook runs Windows 7 and has a recent Thunderbird update?