Cant watch videos...

Hello,
My computer has been acting quite strange lately.I was browsing a site, while suddenly my computer says "Low Disk Space", or something so.I clicked it which directed me to the 'remove program' thing in the control panel.I realized there was nothing to uninstall that took up alot of memory.So, i stupidly erased avast ( one of my security programs) and now when i open i.e, it says " your current security settings put your computer at risk.Click here to change your security settings."And so i did, i went into internet options, security, custom level, and allowed scripts, file downloads and pressed 'ok'.I restarted my computer as told.I opened i.e, went to Youtube, yet i still can't watch videos, unfortunately the enabling that i did in security in 'internet options', did not save. >.< I am really confused and seeking help from all the computer brainiacs out there :P. Thanks.