The main advantage of GPT is a practically unlimited size,
http://en.wikipedia.org/wiki/GUID_Partition_Table, more knowledgeable persons may give more info. Speed shouldn't be an issue, if I have it correctly.
It depends on the disk size you have.
While waiting for better advice, a solution could be to use an outside partition program, like AOMEI
http://www.disk-partition.com/, or GParted,
http://gparted.org/. Windows does have problems with formatting / partitioning.
In this case, the advice would be to boot to the disc via BIOS, delete all partitions, create new ones, perhaps in NTFS form, one partition C for system where you have Windows and crucial programs, big enough, perhaps 80Gb, then one or more partitions for your own files.
That's about all I can say. Hope you get it running.
Might be smart to wait for a day or so, if someone else has something to say.