Right click IE icon on desktop.
Select properties.
On the general tab,
For IE6 select cookies then delete,
Select off line files then delete,
select browser history then delete.
On the security tab select each zone and reset to default if the default button is not greyed out. Click apply to confirm.
Onthe privacy tab again set to default. click apply.
On the content tab, in the personal info section,
click auto comlete,
click clear forms then ok,
click clear passwords then ok.
On the advanced tab,click restore all defaults,
click apply,
click ok.
IE 7 is much the same with the exception of the genera tab,
on off line files click delete then click delete all then ok.
This will stop IE from dropping out,
I do believe you have had a bit of malware changing your settings http://www.microsoft.com and run a malicious software removal tool through your system.
For a generaly slow computer http://www.annoyances.org
Will give you very handy hints and tips to safely speed your system up.
good luck.