unable to send files via browsers

Lately I've run into a head-scratcher of an issue with my PC. I cant send outgoing files to the internet.

I've tried email attachments on Yahoo
I've tried putting up a .rar of my files on rapidshare
I've even tried updating my Beklin router's firmware

Any action involving sending of files via a browser immediately just cuts out and dies, and from then on, I am unable to access any internet or local network (192.168.2.1 in this case) until I restart. This is supported by the fact that my Outpost Firewall Pro is showing a sudden stoppage of all network bytes in/out as soon as I click the "send" or "update" or "attach" button on the browser.

This is confusing as I was able to attach similar files fine not 3 days ago on the same yahoo email account I use.

I've already ruled out router and/or beyond-router issues as I've sent test files fine (scattering of Word .doc's, random jpg's taken off the internet and flipped upside down for sending, and some garbled text files with some legible words at the end) sans the belkin router update, since the laptop I was using (Vista) is one I dont trust to be completely 100% clean enough for the job. Paranoid old me.

Steps I've taken with no success:
*paused, and then stopped internet mail, network and web shields of Avast 4 (failure)
*tried IE7 instead of my addon-using Firefox (fail, same issue)
*tried another PC on the network (laptop, success)
*tried different methods of sending files via browser (rapidshare, fail)
*tried updating Belkin wireless router firmware (fail, could not even get the updated firmware to the router)

 

Additional info:

Even though all browser and internet-related activity stops, I can still ping to the outside world, indicating that there is something wrong in my network settings and not a router-to-PC issue as I first though (which supports the fact that I could send files from my mother's vista laptop on the same network).

Anyone have any ideas? I'm scratching my head over this and its very confusing.

 

Yes, WinXP SP3

Yes, I've tried, its not the firewall. It wouldnt make sense either way since the firewall updated AFTER I found the issue.

I will attempt this if I bump into the issue again

Already done, PC's cleaned out, issue still remains

Tried both, safe mode and/or no addon modes. No change.

Highly unlikely, as this PC is not even 3 months old on this current install and I have Outpost Firewall Pro, Avast 4, and Comodo BOClean all on top of a WinXP SP3 clean install all running on my PC ever since it took its first step online. I have however, taken Avast 4 and the online Kaspersky for spins (seperately of course) and besides the obvious positive in an old file I put in a USB (old DOS virus that I've checked well before the reformat to be unable to infect anything in WinXP) to test I wasnt being faked on the scan, I'm clean.

Still headscratching over this. I am however, following the malware guide just in case something really sinister slipped through even the major walls of protection I've put up. Considering Outpost Firewall Pro asks me for permissions on ANYTHING that wants to run/be referenced/reffered to and not seeing any sort of unknown or unintended activity, I'm probably going to waste time running the malware guide. Still, I'll take a scan and see.

 

I've just checked with SUPERAntimalware and I've checked off as clean. I even used the winsock lsp chain repair thing that was in the guide with no success.

Malware is likely out of the picture in this case. I know its something in, at, or on my PC thats causing the unusual behavior. No idea if its hardware or a software update by one of my programs like Avast, Outpost, or BOClean that's interfering somewhere. The strange bit is that all other internet activity is fine, sans the ISP being a fracktard at times with bandwidth (I'm paying you for 1mbps, not 1Kbps you nimrods!), its just when my browsers start to have to handle sending any files via web pages, my entire network connection goes into massive limbo.

Ping however, works, unusually. Its like something's getting stuck somewhere, and this is supported by Firefox, even when forced to close, will still stay in taskman, indicating something is getting stuck somewhere...

 

short bump. Anyone got any ideas I can work with? Whilst this isnt a showstopper, it is rather disconcerting.

 

bump. Help please