I have a question for you;
First boot into the working OS and press "WINDOWSKEY+R" tpye "msconfig" into the opening box and press the "OK" button.
In the msconfig program, when you switch to the boot-tab (on top, 2nd from the left), do you see your second OS in the big field?
In case you do, this program should enable you to tweak system startup and find a way to get into the 2nd system (If you must).
However; If you have a virus on one OS, it's on the other one too.
If you run an up to date version of the Browser you use, you should be secure against most threats of webpages sneaking in maleware without you noticing it.
The Mangatraders HP looks completely harmless to me.